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Gallery, Projects and General => The Design Shop => Topic started by: BillTodd on November 04, 2010, 11:53:55 AM

Title: Coax indicator design
Post by: BillTodd on November 04, 2010, 11:53:55 AM
This  coaxial indicator design is one I've been working on for a while. The images shown do not include fixings or screwed joints.

 Before I commit it to metal, anyone have any comments on the ball angle changer ?


(http://billtodd.dyndns.org/animations/CoaxInd1.gif)
Title: Re: Coax indicator design
Post by: Rob.Wilson on November 04, 2010, 12:02:51 PM
Hi And welcome Bill .


Great idea/design  :dremel:   ,,sure will take up allot less room with the DTI mounted that way ,,,,,,,,,,,, :med:



Rob  :D
Title: Re: Coax indicator design
Post by: BillTodd on November 04, 2010, 12:14:54 PM
Thanks for the welcome Rob :)

Quote
less room with the DTI mounted that way
That's the whole reason for making it. My little Haighton  (http://haighton.webhop.net)hasn't much room below the vertical head. I wouldn't be able to get a Blake type in there.

However, I can't take credit for the idea, it was inspired by this clever design by PM member Wes43:

http://home.comcast.net/~nonsense91/SALE/Coax%20Ind.JPG (http://home.comcast.net/~nonsense91/SALE/Coax%20Ind.JPG)

judging by the pin to the top/left of the DTI, it uses a lever to turn the movement 90 degrees.

Bill
Title: Re: Coax indicator design
Post by: Bogstandard on November 04, 2010, 01:16:23 PM
Bill,

I use one of the normal ones, and one of it's major faults is the length. In fact, I have made shorter probes to allow me to use it with my RT with the chuck fitted.

I suppose the angled design actually shortens it by over one inch, which has to be good.


Bogs
Title: Re: Coax indicator design
Post by: Rob.Wilson on November 04, 2010, 02:05:44 PM
Hi Bill

Great idea all the same ,,, thanks for showing  :thumbup:  ,,,,,,,,,, must add it to the list  :proj: .

Impressed with your cad drawings  :bow: :bow:   ,, will you be producing some drawings  :poke: :poke:


Rob
Title: Re: Coax indicator design
Post by: BillTodd on November 04, 2010, 03:35:17 PM
Quote
will you be producing some drawings

Yes, assuming it works. ;)

I was expecting (still am) all sorts of criticisms of, and objections to, the ball angle changer

Hi John,

I don't like the idea of getting my hands anywhere near a spinning probe, so I'm wondering about a simple torque limit clutch between the drive and the rocker arm. Does your Blake device have anything like this?

I have also been thinking about a slow speed drive mechanism (which would also double as a clutch), but I'm not sure how to keep every thing concentric. Worth the effort?

Bill
Title: Re: Coax indicator design
Post by: Bogstandard on November 04, 2010, 04:19:44 PM
Bill,

I wouldn't bother with the clutch idea, it has a sort of safety feature because the probe isn't mounted solidly, a bit like a probe on a DTI, if any force at all is put on it, it just moves away.

What isn't there can't go wrong.

I don't know how fast you expect to run it, as when I run mine, having electronic speed control, I run it at around 20-30 RPM, otherwise I find my eyes can't keep up with the bouncing needle. I suppose a sign of getting old.
So maybe a speed reducer would be advantageous to people who can't get their machines to go so low, but in all honesty, it would be a pig to do while retaining concentricity, plus also it would be just liable to increase the overall length, a thing your version scores on.

People have said that they aren't very accurate, but in all honesty, in the time I have been using mine, I could never get anywhere as near to true as the coax gets it, plus the ease and speed of use is fantastic. I used to hate setting up to find concentricity, and started to grow a 2 foot long rubber neck to prove it (just joking of course, it was only 18") but now I really enjoy the complete control I have over the process.

I think Stew has now invested in one, and I think he has the same sort of feedback as myself.


John
Title: Re: Coax indicator design
Post by: BillTodd on November 04, 2010, 05:43:30 PM
Quote
I don't know how fast you expect to run it, as when I run mine, having electronic speed control, I run it at around 20-30 RPM, otherwise I find my eyes can't keep up with the bouncing needle. I suppose a sign of getting old.
So maybe a speed reducer would be advantageous to people who can't get their machines to go so low, but in all honesty, it would be a pig to do while retaining concentricity,

All good points.  My drill/mill requires a belt swap (a right PITA), but I can slow the Haighton with its VFD - you're right no slowmo drive.

Quote
plus also it would be just liable to increase the overall length, a thing your version scores on.
Speaking of which... I've removed the unnecessary top cap (a legacy from an earlier design) which has shaved another 8mm off the height. I think I should save another couple of mm by re-thinking the rocker arm/probe holder.
Title: Re: Coax indicator design
Post by: RichardShute on November 04, 2010, 07:12:34 PM
This  coaxial indicator design is one I've been working on for a while. The images shown do not include fixings or screwed joints.

 Before I commit it to metal, anyone have any comments on the ball angle changer ?


I can imagine a couple of aspects which might be less than ideal - I know, 'misery guts'.

The DTI is operated by riding up/down a conical surface so any radial play between the outer body/DTI mount and the inner shaft will give rise to a false reading. If you were to arrange the DTI to be actuated via a bell crank resting on a flat disc that potential error is removed and you may even be able shorten the whole assembly slightly.
Also, as shown, the DTI (obviously) does not rotate, but it does move up and down to give the reading. You will presumably hold the outer body by hand to stop it rotating and thereby have a very fair chance of inadvertantly raising or lowering it. By re-arranging it a little so that the DTI remained fixed vertically this potential error would be removed.

As it stands, I expect it will probably perform adequately, with care in use, but I think you can still improve the design. You have come this far, why not polish it a little more?

Richard
Title: Re: Coax indicator design
Post by: BillTodd on November 05, 2010, 07:25:37 AM
Quote
I can imagine a couple of aspects which might be less than ideal - I know, 'misery guts'.
Not at all Richard :)

The problem with pixel machining is that everything fits perfectly there's no wobble, no TIR or friction. Without someone to look over ones shoulder it is all too easy to miss the pit-falls.

Here's a perfect example:
Quote
any radial play between the outer body/DTI mount and the inner shaft will give rise to a false reading.

I had considered radial run-out of the shaft,  but assumed I could turn all the bearing surfaces at the same time, so keeping any run-out to a minimum.

I had however, completely ignored body-wobble as the upward force from the rocker moves around the bottom face (cheers Richard :))

I can see a couple of possible ways to minimise the effect without changing the design:

1)The bearing surfaces have to be a very good sliding fit, so I could make them tight then lap them to a good fit.

2)The stay arm (that prevents the body turning) could be hung off of the same side as the DTI thus moving the centre of gravity out towards the DTI. This should apply a (vertical) torque to the body, pre-loading the top and bottom bearings and keeping them snuggled up against the shaft.

Quote
...arrange the DTI to be actuated via a bell crank resting on a flat disc

I looked at bell-cranks or levers (as used in Wes43's example above), but couldn't come up with a neat, compact arrangement. A lever would offer the possibility of some 'gain',  to compensate for losses at the rocker/probe end. Wouldn't it need a gimbal of some sort to remove all radial errors ?
 

Quote
By re-arranging it a little so that the DTI remained fixed vertically this potential error would be removed.

If the DTI/ body is fixed vertically then the problem of wobble & smooth parallel motion perpendicular to the shaft shifts to the rocker follower (IYSWIM) . I couldn't figure how to do fix that.  :scratch: Had you something in mind?

Bill


Title: Re: Coax indicator design
Post by: kwackers on November 05, 2010, 08:33:55 AM
Just to throw something completely different into the mix.

I was contemplating making something like this and so I'm fairly interested in the issues and design.
What I considered doing though to make the whole thing small was to get a magnet to move and use a coil as a pickup (or the other way round). This could be used to drive a small meter. It auto zeroes when not moving (since we're only interested in the 'wobble') and could in theory provide the 'multiplication' required to overcome the mechanical 'loss' particularly when long arms are used.

It's not got much further than an idea, but I thought I'd bung it up here in case it had legs or could give someone a nudge in another direction.
Title: Re: Coax indicator design
Post by: ken572 on November 05, 2010, 11:35:07 AM
Bill,

That is a really cool idea/concept. Time to build a proto-type,
and make a video clip of it in test use.  :thumbup: :clap:

Ken.
Title: Re: Coax indicator design
Post by: picclock on November 05, 2010, 11:56:53 AM
I like the magnet idea.

A multipole magnet with north and south horizontal close to a stereo cassette recorder read head might be an easy way to implement it. Just tuning for minimum output would work. By connecting the heads out of phase the balance between north/south fields would be very precise.

Somthing to think about  :coffee:

picclock

 

Title: Re: Coax indicator design
Post by: BillTodd on November 05, 2010, 12:26:54 PM
Just to throw something completely different into the mix.

I was contemplating making something like this and so I'm fairly interested in the issues and design.
What I considered doing though to make the whole thing small was to get a magnet to move and use a coil as a pickup (or the other way round). This could be used to drive a small meter. It auto zeroes when not moving (since we're only interested in the 'wobble') and could in theory provide the 'multiplication' required to overcome the mechanical 'loss' particularly when long arms are used.

It's not got much further than an idea, but I thought I'd bung it up here in case it had legs or could give someone a nudge in another direction.

I had wondered about using a magnet to couple the rotating vertical movement of the rocker to a stationary lever but rejected it as too compliant.

Quote from: picclock
I like the magnet idea.

A multipole magnet with north and south horizontal close to a stereo cassette recorder read head might be an easy way to implement it. Just tuning for minimum output would work. By connecting the heads out of phase the balance between north/south fields would be very precise.

Somthing to think abou

Yes.

The snag with all magnetic sensors like coils is their sensitivity to stray fields (hum from motors or just the rotating mass of iron coupling to any static magnetic field. I suppose if the parts could be shielded it might work

Or (getting excited now :LOL:) if there were four coils, stationary and located on the X  and Y axis.  With two magnets on the rocker, as they passed the coils, each magnet would induce a different current in the two coils (varying with distance). it would be possible to synchronously rectify the outputs of the two pairs of coils to give an X & Y error read out. Thoughts?



Title: Re: Coax indicator design
Post by: Bluechip on November 05, 2010, 01:04:03 PM
Some more 'orrible thoughts ... if you want to convert a wobble to a indicator ( meter ? ), you're making a seismometer. :thumbup:

Some 30 yrs ago I made ' variable capacitor / pll / amp / meter contraption that actually worked.

The cap was two bits of PCB, one bit stationary, t'other attached to a weighted beam. When it moved, capacitance varied, osc. freq. likewise, pll outputs a voltage proportional to freq. and so to the amp.

Maybe easier to screen than inductors/ magnets. Maybe not.

Dave BC

PS .... don't ask how I configured the pll, 'cos I can't remember. Only time I've ever used one   :scratch:

It was not a 4046 IIRC. NE xxxx ?? But it is probably possible with a 4046. Suppose they're much the same.




 
Title: Re: Coax indicator design
Post by: kwackers on November 05, 2010, 01:16:49 PM
I was thinking of a low impedance coil, i.e. just a few turns around the (ali?) body. It would have very little susceptibility to mains hums and stray magnetic fields (I think) would be too low by the time they got there, it could also (probably) drive say a 50uA meter directly.
Title: Re: Coax indicator design
Post by: RichardShute on November 05, 2010, 03:13:24 PM
Just to throw something completely different into the mix.

I was contemplating making something like this and so I'm fairly interested in the issues and design.
What I considered doing though to make the whole thing small was to get a magnet to move and use a coil as a pickup (or the other way round). This could be used to drive a small meter. It auto zeroes when not moving (since we're only interested in the 'wobble') and could in theory provide the 'multiplication' required to overcome the mechanical 'loss' particularly when long arms are used.


The problem with that is that as you say you get no output when the magnet is not moving and with the relative speed being ineviably very slow you will get negligible output. You'd be much better using a LVDT (linear variable differential transformer) which are readily available to buy (for *real* money) or could be made. It is basically two colis on a common former with a magnetically susceptible slug up the middle attached to the probe. You apply a signal to one coil and compare it with the other. They can be easily accurate to a micron!

Bill
I have some ideas for a reasonably non-rocking slide scheme, I'll try to do some sketches shortly.... Not got time just now - off out to pickle some brain cells.

Richard
Title: Re: Coax indicator design
Post by: AdeV on November 05, 2010, 03:56:08 PM
The downside to all this coil malarkey, as I see it, is you're going to need to introduce circuitry and batteries 'n' stuff. But, if you're going to do that, wouldn't it be easier to use a hall sensor? As the magnet moves up & down in the unit, its distance from the sensor will vary, and (in theory at least) you can then read off the distance between magnet & sensor as a voltage output. This also means you can take a reading while everything's stationary, should you so desire. I don't know how easy/difficult it would be to use 2 hall sensors to get X & Y readings...
Title: Re: Coax indicator design
Post by: picclock on November 05, 2010, 05:29:23 PM
@ kwackers
even 3000rpm is only 50 hz which is a quite a low frequency for what you are suggesting, hence my suggestion of multiple poles to increase the frequency. At 100 rpm you would need some serious core material - which would make it quite large. :scratch:

@billtod
at 50 rpm (just under 1 Hz) the frequency of wobble would be so low that filtering out the other induced interferance would be simple. Additionally, if it was encased the case would act as a faraday shield. But .. .

@bluechip
PLL is probably the best approach. Change of capacitance would be very small though and overall capacitance would be low, so high frequency needed. 4046 sounds just the job. Power it and a moving coil meter with 2 or 3 button cells, add some form of off on switch and it should be good to go.

It's quite a good idea that ought to succeed. :clap:

Just needs a reasonable mechanical design.

One for the 'tuit' list. :beer:

picclock


 




Title: Re: Coax indicator design
Post by: kwackers on November 05, 2010, 08:44:19 PM
@Picclock, yeah I always forget rpm and hz aren't interchangeable! That means my simple version is a non-starter... :doh:
Title: Re: Coax indicator design
Post by: BillTodd on November 06, 2010, 02:19:17 PM
Well Today I turned up a few of the parts....

The shaft and DTI holder are 316 stainless, the body is in an unidentified bronze. I'm pleased with the fit of the shaft, but I'll have to drill an air hole in the middle 'cos the thing acts like a piston pump ATM.

Tomorrow, I'll fire-up the milling machine.
Title: Re: Coax indicator design
Post by: BillTodd on November 07, 2010, 12:11:39 PM
What's that saying about best laid plans...

I was only able to assemble the the parts I had already made. The mechanism seems to work OK, I get about 0.12" of indicator movement between the top and bottom positions of the shaft.
Title: Re: Coax indicator design
Post by: Brass_Machine on November 07, 2010, 11:59:30 PM
The turning work looks good. Anxious to see how this works out for you.

Eric
Title: Re: Coax indicator design
Post by: RichardShute on November 08, 2010, 06:15:50 AM

I was only able to assemble the the parts I had already made. The mechanism seems to work OK, I get about 0.12" of indicator movement between the top and bottom positions of the shaft.

Looks like you are making a nice job of it Bob. Sorry I didn't have time to offer my suggestions over the weekend, I got bogged down in domestic drudgery... and now you are well on the way with your own design, I don't want to distract you from your purpose.

I'll watch with interest.
Rgds
Richard
Title: Re: Coax indicator design
Post by: BillTodd on November 08, 2010, 06:59:14 AM
Quote from: Eric
The turning work looks good. Anxious to see how this works out for you.
Yes, my Hardinge makes it look like I know what I'm doing  :thumbup:

Quote from: Richard
Looks like you are making a nice job of it Bob.
I'm sure Bob will make a far better job of it than I ever will :)

Quote
...I don't want to distract you from your purpose.
Don't let that stop you ;) I already have ideas for a second version, I'd love to see what you had in mind.

Bill
Title: Re: Coax indicator design
Post by: BillTodd on November 08, 2010, 02:26:31 PM
Rocker on  :headbang:

Managed to get the slot cut and the rocker made.

I was wondering how to grind the involute curve on the tips of the rocker when this idea struck...

I stuck a disc of emery to the bottom of the indicator body, assembled the lot into the lathe chuck, then ground the tips in situ :)

Title: Quickly centring a rotab
Post by: BillTodd on November 08, 2010, 02:35:24 PM
I thought you might like to see how I quickly centre my rotary table.

I found a expanding clamp, the type used to fix pulleys to shafts, that conveniently fits the MT3 hole in my rotab and fits the 10mm end of my little edge detector.  

I can pop the clamp in to the hole in the rotab, lower the edge detector in to the clamp, nip it up finger tight, then by either sighting or feeling the two parts of the edge detector , I can align the centre to about 1 thou" or so.
Title: Re: Coax indicator design
Post by: RichardShute on November 08, 2010, 06:48:17 PM

Quote from: Richard
Looks like you are making a nice job of it Bob.
I'm sure Bob will make a far better job of it than I ever will :)


Bill
Bugger! Well I knew who I meant, just a keyboard problem. Appologies...

I'll nut out some sketches of some sort for interest, maybe for the Mk2.

Richard 
Title: Re: Coax indicator design
Post by: BillTodd on November 09, 2010, 03:52:45 PM
Almost ready to test...

Made the little probe holder this evening. The plastic wheel in the photo will be replaced later with a lever (I think).

Bill

Quote
I'll nut out some sketches of some sort for interest, maybe for the Mk2.
Sounds good :)

John, Does your Blake device have a spring to bottom the body, or does it, like mine, rely on weight?
Title: Re: Coax indicator design
Post by: Rob.Wilson on November 09, 2010, 04:23:07 PM
Hi Bill

I like the way you ground the tips  :med:  ,,,,,,,,, looking forward to seeing it in action  :thumbup:


Rob
Title: Re: Coax indicator design
Post by: BillTodd on November 10, 2010, 02:54:07 PM
Well that seems to work OK  :)

Made a little screw to clamp the probe onto the rocker (worked at second attempt having bent the first one  :hammer:)

Made a simple hook using a 3mm rod and a magnet from a small loudspeaker to hold the indicator still. Then, gave it its first test...

http://www.youtube.com/watch?v=wQYw0c3RN_0 (http://www.youtube.com/watch?v=wQYw0c3RN_0)

There's a residual ~1/2 thou" wobble caused, I think, by the face out of alignment with the bore. The facing had to be a second operation because of the dual diameters of the bore - I may have another go at it, taking more care this time (MkII will have a straight bore) .

I also noted a tiny 'kick' with the thing zeroed on the mill, the cause of which I have not been able to find - could be a piece of **** in the taper part or ???

Bill



Title: Re: Coax indicator design
Post by: andyf on November 10, 2010, 03:27:39 PM
That's terrific!
:clap: :clap: :clap: :clap: :clap:

Andy
Title: Re: Coax indicator design
Post by: bp on November 10, 2010, 04:11:47 PM
Excellent!!
cheers
Bill Pudney
Adelaide, Australia
Title: Re: Coax indicator design
Post by: j45on on November 10, 2010, 04:26:54 PM
Very nice job  :bow:
Title: Re: Coax indicator design
Post by: Rob.Wilson on November 10, 2010, 05:45:11 PM
JUST THE JOB , nice one  :bow: :bow: :bow: :bow:

Rob
Title: Re: Coax indicator design
Post by: Rob.Wilson on November 10, 2010, 05:52:34 PM
 :offtopic: but just a thought  ,, i was thinking of using the ball from  piercing barbells for the end of the probe ,, they are stainless steel , come in a range of sizes and have a threaded hole  :med:  ,
http://en.wikipedia.org/wiki/File:Piercing-Barbell.jpg

Rob
Title: Re: Coax indicator design
Post by: bp on November 10, 2010, 08:16:30 PM
Somewhere for a similar application, I'm pretty sure that I've seen someone using balls from ball bearings sat in a little recess, retained by Araldite, or Loctite.  Could even soft solder them, the temperature wouldn't be high enough to affect the hardness of the balls.  Balls are available from bearing stockists at an amazingly low price for such a precision item.
Cheers
Bill Pudney
Adelaide, Australia
Title: Re: Coax indicator design
Post by: Divided he ad on November 10, 2010, 10:40:17 PM
Bill....  :jaw:  :bow:  :bow:  :bow:  :beer:


Well, that's just great (not sarcasm) made with pace too!  0.5 thou wobble!!! Not a bad tolerance for the prototype eh?


Very impressed  :clap:





Ralph.
Title: Re: Coax indicator design
Post by: Brass_Machine on November 10, 2010, 11:27:39 PM
Wow.  :bow:

Not only does the prototype work fairly well, it looks fantastic. Looking forward to MK2

Good job sir

Eric
Title: Re: Coax indicator design
Post by: Bogstandard on November 11, 2010, 12:43:02 AM
Bill,

Methinks you've got it nailed.

Very well done.

I honestly don't think you need to make a Mk 2, just turn up a close fitting internal mandrel and gently skim the end of Mk 1. You should only be removing about a thou, so a tiny spot of superglue should hold it.

BTW, you have really shown with your vid how easy these tools make setting up finding centre really is. It used to take me ages to do it the normal way with a DTI, even the act of turning it by hand used to deflect the needle slightly, my coax tool was a true revelation when I first started to use it.


Bogs
Title: Re: Coax indicator design
Post by: sbwhart on November 11, 2010, 01:35:18 AM
Great work Bill.

I've got a trade bought Coax and its a bit on the long side for my machine I had to make a special collet to get it fitted, but this design being shorter would be a lot more convenient.
 
:clap: :clap: :clap: :clap: :clap:

:thumbup: :thumbup: :thumbup: :thumbup: :thumbup:
 

Stew
Title: Re: Coax indicator design
Post by: BillTodd on November 11, 2010, 04:58:37 AM
Thanks Guys  :D

Rob, I like your bar bell idea - It'd save me having to rig up a ball turner.

bp, Another good idea - The ends of my other indicators have a ball in a pocket as you suggest.

Bogs, I like the mandrel idea. I don't need to face all the way to the centre, so I can set the thing between centres.

The aim of a MkII version would be simpler/easier construction and/or more accuracy. I have yet to test the centring with another DTI but judging only by the feel of the handles it no better than +/- 1 or 2 thou"; There's about a 3:1 loss between the probe/rocker and the DTI so 1 thou" on the indicator could be 3 at the work piece.

Bill
Title: Re: Coax indicator design
Post by: kwackers on November 11, 2010, 07:59:17 AM
Bill,

I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?

(Nice job btw!)
Title: Re: Coax indicator design
Post by: slowcoach on November 11, 2010, 11:51:27 AM
Brilliant  :clap: :clap:

Rob  :thumbup:
Title: Re: Coax indicator design
Post by: BillTodd on November 11, 2010, 12:38:48 PM
Bill,

I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?

(Nice job btw!)

ATM 10thou" of displacement caused and indicated 3 thou on the DTI (which would be doubled as run-out). I suppose a quick improvement would be to swap the cheap DTI for a tenths indicator.
Title: Re: Coax indicator design
Post by: winklmj on November 11, 2010, 01:59:48 PM
Amazing...design to Mk1 in 6 days. I want one.
Title: Re: Coax indicator design
Post by: BillTodd on November 11, 2010, 04:34:45 PM
Ok here's the MkII provisional design

A straight shaft should be easier to make and means the critical parts of the body, the bore and face, can be machined in one operation.

Bill

Title: Re: Coax indicator design
Post by: mklotz on November 12, 2010, 01:07:45 PM
Bill,

Can I encourage you to provide a few measurements for your design, please?  Just the main shaft and the bronze sleeve ought to cover it.
Title: Re: Coax indicator design
Post by: BillTodd on November 12, 2010, 03:28:32 PM
Bill,

Can I encourage you to provide a few measurements for your design, please?  Just the main shaft and the bronze sleeve ought to cover it.

No problem Marv

The attached drawing are for MkI - I'm sure you can extrapolate to the MkII if you need to :)

The drawings are as designed rather than as made so, for instance,  I made the large diameter of the shaft 19mm (~3/4") because the A4 bolt I used as stock would not quite give me 20mm once surfaced. If it's easier to make the 15mm diameter = 5/8" or the 10mm = 3/8" , it won't make any difference to the function of the device.

The bearing ball I used was 5mm but  3/16" or even 1/4" would do, just adjust the holes to suit.

I machined the indicator holder to be a press fit into the side of the body - might have been better to thread it.

Title: Re: Coax indicator design
Post by: mklotz on November 12, 2010, 04:54:38 PM
Many thanks, Bill.  I have a broken Chinese clone of a Blake that I'll cannibalize for probe and rocker.  It will be satisfying to turn the junk into a useful tool.
Title: Re: Coax indicator design
Post by: BillTodd on November 13, 2010, 05:56:23 AM
Post picture of the conversion  :worthless:
Title: Re: Coax indicator design
Post by: BillTodd on November 15, 2010, 12:28:25 PM
Kwackers had a good idea in another forum. Adding a spring and ball to push the body towards the rocker so it can be used horizontally. It will also pre-load the shaft so reducing any wobble caused by the force from the rocker.


Title: Re: Coax indicator design
Post by: winklmj on December 04, 2010, 10:44:29 PM
What are you making your probes out of? I scored a used Blake off of Fee-Bay sans the probes. I made a straight one out of some bronze. Would hardened drill rod be any better?

The Blake eats up a lot of Z-axis so one of yours is on my project list.
Title: Re: Coax indicator design
Post by: BillTodd on December 05, 2010, 07:44:27 AM
I think it was a piece of silver steel, but anything reasonably stiff would do.  Drill rod would be perfect :)
Title: Re: Coax indicator design
Post by: winklmj on December 05, 2010, 07:16:07 PM
Made a curved one out of bronze again and tried it. Just one use against a piece of aluminum had put a tiny flat spot in it. So I made some out of drill rod and hardened the tips:

(http://i119.photobucket.com/albums/o152/wavedudetx/MetalProjects/IMG_2790.jpg)

Freehanded everything so there are some goofs but the ball-ends are pretty smooth.
Title: Re: Coax indicator design
Post by: Bezalel on May 02, 2011, 08:48:30 PM
a little late to jump into this thread maybe, but I've only just  seen it. and  must say I realy like it  :clap:

Quote
Bill,

I know this depends on the length of the bar, but in the configuration shown what sort of displacement of the meter do you get for say 1 thou of error?

(Nice job btw!)


ATM 10thou" of displacement caused and indicated 3 thou on the DTI (which would be doubled as run-out). I suppose a quick improvement would be to swap the cheap DTI for a tenths indicator.

I'm thinking when I build my own I will be looking at reducing or eliminating the  resolution reduction of 3:1

by this I mean it seams to take 3 thou movement on the job to register 1 thou on the dial.

The length of the pickup has significant bearing on this

(http://i1095.photobucket.com/albums/i461/Bezalel2000/Coax_ind_1.jpg)

If the probe length is adjustable to approx half diameter of the job and rotated to be horizontal, such that it is pushed end on, the acuracy of the dial increases accordingly.

for unity resolution of the dial or better. can anyone think of any reason this couldn't be done here?

(http://i1095.photobucket.com/albums/i461/Bezalel2000/Coax_ind_2.jpg)
Title: Re: Coax indicator design
Post by: BillTodd on May 03, 2011, 07:23:50 AM
Quote
If the probe length is adjustable to approx half diameter of the job and rotated to be horizontal, such that it is pushed end on, the acuracy of the dial increases accordingly.

Yes, sort of. To work out the exact ratios you'll need to work out the effective lengths of the levers rather than the actual the lengths of the levers, but in principle the shorter the  measuring arm the more the dial will move for a given displacement.

Another way to increase sensitivity, would be to change the angle of the taper on which the ball runs; If this were greater than 45° it would push the DTI slide further (you will need to stick with my original stepped design to ensure the ball is supported on the other side of the taper). It may even be possible to use a curved taper to compensate for the change in lever angle.


Alternatively, it would not be impossible to make a compound lever mechanism to increase sensitivity , as Richard Shute suggested earlier.
Title: Re: Coax indicator design
Post by: bp on May 03, 2011, 05:22:08 PM
I've been a'wondering about this for a while.
"Wondering 1".... was to use a DTI rather than a Dial Gauge and run the probe on the lower face of a groove in the main shaft.  The ultimate version of this used a washer from a thrust bearing, as they are ground flat etc etc
"Wondering 2".... was to use a cranked lever to activate the Dial Gauge, as has been previously mentioned.  Fiddle about with the ratios to get a more favourable stylus movement/indicator movement ratio
"Wondering 3".... Bill, in your last version, the one with a ball riding in the groove, the side loads on the indicator must be considerable, or is the indicator probe well located so that it can only move in and out, if you see what I mean?
cheers
Bill Pudney
Title: Re: Coax indicator design
Post by: BillTodd on May 04, 2011, 04:54:46 AM
I've been a'wondering about this for a while.
"Wondering 1".... was to use a DTI rather than a Dial Gauge and run the probe on the lower face of a groove in the main shaft.  The ultimate version of this used a washer from a thrust bearing, as they are ground flat etc etc

Yes, that should work well
Quote
"Wondering 2".... was to use a cranked lever to activate the Dial Gauge, as has been previously mentioned.  Fiddle about with the ratios to get a more favourable stylus movement/indicator movement ratio
A lever is certainly possible (the DTI above has this same lever built into the device)

Quote
"Wondering 3".... Bill, in your last version, the one with a ball riding in the groove, the side loads on the indicator must be considerable, or is the indicator probe well located so that it can only move in and out, if you see what I mean?
cheers
Bill Pudney
The only side load on the indicator, that I can see, is from the friction with the ball as it spins (if it spins?) which is lubricated with a hardened point contact. I don't think it's a cause for great concern .

Bill
Title: Re: Coax indicator design - FOR SALE
Post by: BillTodd on September 26, 2011, 06:54:47 AM
I have decided to put my prototype indicator up for auction on ebay to raise money for the Royal British Legion's 90th anniversary appeal.

http://www.britishlegion.org.uk/support-us/how-to-give

It should be listed by Thursday (I'm just waiting for the Ronseal to dry on the wooden box - posh or what  :headbang: ) all the profits will go to the charity (I'll pick-up the auction and paypal fees, the winner will pay the postage).

Title: Re: Coax indicator design
Post by: slowcoach on September 26, 2011, 10:56:34 AM
A very worthy cause  :clap:

Title: Re: Coax indicator design
Post by: BillTodd on September 26, 2011, 03:04:00 PM
A couple of pictures of it in the box:

Title: Re: Coax indicator design
Post by: BillTodd on September 27, 2011, 07:24:46 AM
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200657351320

ebay auction is now active you have ten days to bid :)

I've started it at 99p (I'd like to see an early bid of at least a tenner ) .

Bill
Title: Re: Coax indicator design
Post by: Divided he ad on September 30, 2011, 03:12:42 AM
Looks like it's going well Bill.... 7 days left and £51 already!! got to be worth well over the £100?  :thumbup:


I haven't the funds for even the £50 but it's a great job in the building and then the selling on   :bow: :clap:



Hope it goes for stupid amounts of hard cash  :headbang:





Ralph.
Title: Re: Coax indicator design
Post by: BillTodd on October 07, 2011, 02:27:44 PM
Well, it sold for £72,  which I think is excellent  :headbang:

I don't know if Ralph, the buyer, is a Madmodder or not but many thanks Ralph. It'll be on its way tomorrow or, if the post office is closed, Monday .

I hope you'll find it very useful :cheers:


Thanks to all those who bid and gave support :)

Bill
Title: Re: Coax indicator design
Post by: woodguy on October 07, 2011, 02:34:00 PM
Well done Bill.

What does the current incarnation of the design look like?
Title: Re: Coax indicator design
Post by: Xldevil on October 07, 2011, 03:43:58 PM
Well, it sold for £72,  which I think is excellent  :headbang:

I don't know if Ralph, the buyer, is a Madmodder or not but many thanks Ralph. It'll be on its way tomorrow or, if the post office is closed, Monday .

I hope you'll find it very useful :cheers:


Thanks to all those who bid and gave support :)

Bill




Of course I am,Bill.
Hope You'll offer me some help if needed.
Cheers,Ralph
Title: Re: Coax indicator design
Post by: HS93 on October 07, 2011, 07:32:54 PM
Well, it sold for £72,  which I think is excellent  :headbang:

I don't know if Ralph, the buyer, is a Madmodder or not but many thanks Ralph. It'll be on its way tomorrow or, if the post office is closed, Monday .

I hope you'll find it very useful :cheers:


Thanks to all those who bid and gave support :)

Bill


Have you thought of making a few more ? I was the out bid at £70 ish via some one was biding for me, but if there where some otheres being made i would be able to save up if they where a bit more expensive.

peter
Title: Re: Coax indicator design
Post by: BillTodd on October 11, 2011, 03:24:19 PM


Of course I am,Bill.
Hope You'll over me some help if needed.
Cheers,Ralph

Always happy to help, Ralph. Just ask :)
Title: Re: Coax indicator design
Post by: BillTodd on October 11, 2011, 03:27:43 PM


Have you thought of making a few more ? I was the out bid at £70 ish via some one was biding for me, but if there where some otheres being made i would be able to save up if they where a bit more expensive.

peter


I'll have to get my second Haighton Miller (http://haighton.webhop.net/page19.html) up 'n' running first and then find a source of cheap bronze & SS etc. etc.

Title: Re: Coax indicator design
Post by: BillTodd on November 02, 2011, 09:20:32 AM
Just a qucik update:

Missionfish, the company that runs the ebay charity donation system have finally taken the money from my paypal account.

However, it appears that The Royal British Legion will not actually receive the donation until December 30th (a 45day delay to allow refunds, apparently). I can only hope Missionfish give a proportion of the interest accrued on their holdings  to the charities (else I'm not sure I'd use the ebay method again!)

Bill
Title: Re: Coax indicator design
Post by: Davo J on November 05, 2011, 06:30:51 AM
Bill, this may interest you
http://madmodder.net/index.php?topic=6246.new#new

Dave
Title: Re: Coax indicator design
Post by: BillTodd on January 14, 2013, 07:13:20 AM
Coax V2 coming soon....
Title: Re: Coax indicator design
Post by: zimma on January 14, 2013, 08:09:23 AM
Hi chaps,

Just a quick hint for those of us with limited Z clearance, or with a round column mill that loses accuracy when changing the height of the head (because of that limited clearance).

I have an MT3 spindle in my mill. If I use a 10mm MT3 collet to hold the coaxial indicator directly in the spindle, and not in a chuck mounted in the spindle, then the touchdown point of the indicator probes is pretty similar to the touchdown point of an endmill in a collet chuck.

I had always struggled with Z axis travel as I used to just swap the coaxial indicator directly for an endmill in my ER32 chuck until i realised I could gain the whole length of the ER32 chuck by mounting the indicator directly in the spindle with a collet.

Hope this helps

Graham
Title: Re: Coax indicator design
Post by: BillTodd on January 14, 2013, 09:02:06 AM
Hi Graham,

Good advice :)

The coax indicator above was designed to work with my Haighton  (http://"http://wktodd.webspace.virginmedia.com/major/")mill which has even less Z clearance than my RF30*.

Even if made a collet for the Int30 spindle taper a normal Blake's type coax is too tall to be of any use. The one above sticks out about 3" from the chuck with the shortest probe.


Bill

*incidentally, I have fixed my round post problem with a wish-bone stabiliser (http://wktodd.webspace.virginmedia.com/drillmill/page4.html)
Title: Re: Coax indicator design
Post by: rotorhead on January 14, 2013, 05:33:52 PM
Hi Bill,

That is very similar to a swash-plate stabilizer, found on many a helis' rotorhead.

Chris
Title: Re: Coax indicator design 2
Post by: BillTodd on January 21, 2013, 04:42:29 PM
I don't have the time/heat to get on with this ATM.

I've already sent these drawing to a chap who's going to try making it, so if anyone wants to have a go feel free :)

Oh and don't forget to post pictures...

 
Title: Re: Coax indicator design
Post by: Divided he ad on January 22, 2013, 07:03:20 PM
Bill,

I picked up 2 x 1" dia DTIs a while back .001 and .0001 IIRC?

So, I've pinched a copy of your plans and will hopefully find some accuracy and  talent, then have a go at it  :)


If I get it going I'll be sure to take and post pic's  :thumbup:





Ralph.
Title: Re: Coax indicator design
Post by: BillTodd on January 23, 2013, 07:42:00 AM
Let me know if there's anything on the drawings that need altering.

Bill
Title: Re: Coax indicator design
Post by: Divided he ad on January 24, 2013, 11:50:20 AM
Bill,

Could be a while, But If I do I'll be sre to let you know  :thumbup:






Ralph.
Title: Re: Coax indicator design
Post by: BillTodd on June 23, 2020, 04:51:58 AM
Now showing on YouTube  :)


Title: Re: Coax indicator design
Post by: Sea.dog on June 23, 2020, 05:09:54 AM
Better late than never, Bill  :clap: