Another 6 x 26 Knee Mill CNC conversion

[John Stevenson]

Starts off "Do not place in the sunshine room "

Best one I saw was on a parts list, it listed Part No.#1234 as Water Buffalo.
Had a look for Part No.#1234 on the illustrated parts list and it was a Hydraulic Ram !!   

[9fingers]

Its been a while since I posted but I have been busy designing and starting to make parts.

One of my design criteria is to retain manual operation via the handwheels and the built in dials from the original machine which are 4mm per turn.
The new ballscrew is 5mm pitch and is right handed. The drive is therefore require to correct for these 'challenges'

This is a cross section through the Y axis drive.



At the top left is the new ball screw supported by a pair of AC bearings. The screw spindle has a 26 tooth HTD pulley secured by grubscrews and to this is bolted a 25 tooth 2 module spur gear. This gear meshes with a home made anti backlash 20 tooth gear which drives the handwheel and original dial.

The gears both correct the pitch ratio and provide a reversal of rotation.

The 26 tooth pulley is connected to a similar pulley (1:1 ratio) via the belt. The lower HTD pulley has been bored to take a needle roller bearing and is free to rotate on the motor shaft.
A simple pin clutch is permanently driven by the motor and when the spring loaded pin is engaged by pulling and rotating the knob by 90 degrees picks up on one of the 4 holes in the pulley.

Now for the pics

The top htd pulley showing the recess for the AC bearing preload adjustment nut



View of the other end showing the 25 tooth gear




This is the completed clutch mounted on a dummy motor shaft



and the component parts.

Dummy shaft - not pretty but functional for testing



The lower HTD pulley with needle roller and four holes for the clutch pin.



This is the driven part of the clutch with the pin withdrawn



and with the pin in the locked position



The external view of the clutch with the pin withdrawn.



Rotating the pin by 90 degrees allows the clutch to move to the engaged position.

This is the sprung loaded pin and the knurled operating knob which also acts a cover for the mechanism.




The two spur gears were purchased ready made ( life is too short!) from  http://www.technobotsonline.com/ and arrived next day!

The teeth are 20mm wide and I parted the 20 tooth one into two halves and machined the recesses for the torsion spring.



The spring installed



and the two halves re-assembled



After parting off and cleaning up the tooth width is 17.5 mm so I reduced the tooth width on the 25 tooth gear to match.
I've yet to see how effective the antibacklash device is. The spring allows about half a turn (10 teeth) maximum so reasonable scope for adjustment.


I've shown the details for the Y axis here but there are similar requirements for the X axis.  The only difference being the the original X feed screw is the same hand as the ballscrew and so the geared drive is not required.  Instead, the 5:4 ratio is provided by a 30 & 24 tooth htd belt on the right hand end of the table and a 1:1 motor drive will be fitted on the left hand end

Thanks for looking.

Bob

[Rob.Wilson]

very interesting Bob ,, clever bit of design work 


Rob

[loply]

Hi Bob,

Real nice bit of work. Question - Is the clutch pin tapered so that it will always achieve a tight (zero backlash) fit?

Are you confident you won't have backdrive issues since you're using ballscrews here? It's quite a big mill to have manual handles on ball screws...

Cheers,
Rich

[9fingers]

Hi Rich,

Yes, the pin slides in a reamed hole and has a 2 degree taper and locates in a parallel hole. My aim was for minimal backlash, automatic take up for wear due to the spring loaded pin and yet trying to avoid it jamming due to the taper. Time will tell how that all works out.

To be honest I don't know if back drive will be a problem or not. I've read conflicting reports. I'm very much a beginner in all this and once I become more proficient in using the CNC, I expect to use manual mode less. I can always nip up the carriage locks a bit?
At the moment it take me longer to draw an item fully than make it. That hopefully will change
What I really need is a back of envelope to gcode interpreter 

Bob

[loply]

Bob,

I needn't have asked about the taper really 

It's interesting that you've made manual mode possible. I'm converting my lathe to CNC at the moment and plan to do my mill at some point and initially wanted to retain manual mode.

Having thought about it I decided against - Using the CNC software you can essentially operate in 'manual' mode anyway by simply jogging the axes using the keyboard, the difference being you can set the jog speed precisely and you get a DRO for free.

The only downside is that the PC needs to be turned on and it won't work if you have an electrical fault, so the mechanical backup is good in that respect!

Cheers,
Rich

[Rob.Wilson]

were be these photos you promised Bob   

Any how , still moving crap around in the shop today , found dis .





Any good to you ? 


Rob

[DaveH]

Bob,

Very nice work 
 
DaveH

[9fingers]

I've been in the wood workshop today - that is my excuse anyway!
Thanks for your offer Rob - I'll send a pm next.

Ok So I've now got an ever increasing selection of parts made most of which seem to fit 



Firstly a couple of the clutches that connect the stepper motor to the htd pulley or not depending on the position of the knob.

These are fixed to the motor shaft and supported by an oil seal which should keep swarf out of the mechanism hopefully.

Next the ball nut housings:-
X axis which needs the odd shape to fit under the table



and the simpler Y axis one where there is plenty of room




This is the X feedscrew extension which enabled me to save the cost of having custom machining done on the screw.



This is the X motor mount, clutch housing and belt drive which will fit on the left hand end of the X screw via the extension above



It needs a 75mm spacer block to keep it out of the way




and the complete assembly less motor to put it in context



When fitted the spacer is at the top and the motor to the rear of the table - again to keep it out of the way.

The X axis handwheel end has the 4:5 ratio belt drive and fits to the right hand end of the table. It is narrow enough to tuck inside the saddle and not limit the X travel.



the two lugs at the top mount onto the table end casting.

The Y axis addition shown below comprises the functions of the both the above parts

Motor mount, clutch, 4:5 ratio drive to the handwheel complete with direction reversal anti-backlash gear and a 1:1 drive to the Y axis feed screw.



and



Kicking around in the parts box are the inevitable spacers and bushes




I'm just waiting for the feedscrews to arrive from Zapp and do a trial fit of a few parts and then to take the table, saddle and knee off my mill and take them over to a friends workshop so I can do some machining on them to mount the ballnut carriers and anything else I've forgotten to do.


In a few weeks, I hope to have it all back together and usable as a manual machine once more whilst I think about the electrical/electronic aspects of the project. I have some other stuff to sort out then and might not be back on this project till after Christmas

Cheers

Bob

[Rob.Wilson]

    Dam fine machining Bob 

You have been busy  worth the wait  , i like your design to keep the manual operation of the machine ,clever 


Rob 

[Brass_Machine]

I agree Bob... That looks pretty darn good!

Eric

[9fingers]

  Dam fine machining Bob 

You are very kind Rob but its nowhere near the quality of your work. 

Bob

[9fingers]

Thanks Eric - I'll pay you later OK?

Bob

[AdeV]

  Dam fine machining Bob 

You are very kind Rob but its nowhere near the quality of your work. 

It's not that, you're not using the special filter that Rob has on his camera, the one that removes machining marks & makes everything look like it was chrome plated.... 

[John Stevenson]

Bloody hell have I got to buy 'another' Juju doll ?

[Ned Ludd]

John, I think you will find they are more effective if you make your own, commercial ones are never the same as home grown, or am I thinking of Tomatoes?
Ned

[9fingers]

Bloody hell have I got to buy 'another' Juju doll ?

I thought you must have a second one already? The fcuk-up fairy has been hovering around my workshop during the build.
I had terrible trouble with some M6 taps that just would not cut any perceptible depth of thread in clearance holes the other day

Bob

[John Stevenson]

Funny that, i sometimes get the same problem but just by a fluke I discovered that the oversize hole is the *exact* right size for a helicoil, Phew, another ones lives another day 

[9fingers]

Good Tip John- Thanks

Bob

[9fingers]

I'm kicking my heels a bit on this project at the moment waiting for parts.

Zapp say they will send out my ballscrews & nuts on Monday so until then I'm thinking about lubrication.

Just made up these to fit pipes onto  the ball nuts and a for instance oil adapter to screw into various places for oiling the ways.

The brass banjos have got little o rings set in the faces as I could not find my little stash of Dowty seals and I have  whole baccy tin of 5/16 x 7/16 O rings that I could find!



I expect I'll use clear pipe finally but just grabbed some black pneumatic nylon to check the fit as it was handy.

Lets hope posty is early on Tuesday!!


Cheers

Bob

[9fingers]

Heels duly kicked for a while and now I have the ball screws and nuts in from Zapp.


Here is the nut fitted to the Y axis mount



Space is very tight on the X axis and earlier in the thread, I found that I needed to trim a bit of the nut flange.
I spoke to Zapp who assured me that the flange sa simply for mounting and did not contain any of 'the works'
They failed to mention that the flange is hardened however.

Sensitive souls should look away now.......




Time to get out the angle grinder

Lots of masking tape around the whole nut apart from the corner of the flange - it looked like it was going into an operating theatre!
Wet cloths handy to cool the patient brow at regular intervals

One of those ever so handy 1mm thick cutting discs and away I went.  Sorry no video clips just an end result.



One final last check though the parts I'd made to make sure I had not further need for a working mill and the strip down starts ready to machine the saddle & knee castings on a friends mill next week.


Bob

[9fingers]

I spent Monday in my mates workshop attacking my Myford VMC castings on his Myford VME
It was a full day and I did not take any pictures of work in progress.
Making a bit more room for the X axis nut in the underside of the table was a bit of a pig with hard spots knocking the edges of the cutter so in the end the angle grinder was the only answer and then back to the mill. I only had to take of 2mm but it took about 2 hours

This morning I started the assembly. In with the Z axis screw. Another tight spot is in the knee and I needed a bit more room over the top of the Z axis gear to allow the Y ball nut to pass over the top.
I ended up by putting a 2mm washer (black one in the photo) under the thrust bearing.



Above the thrust bearing there is a spacer and needle roller bearing.



The spacer is an addition as the original arrangement allowed the helical gear to rub on the knee casting. This can't happen with a spacer fitted.

On with the knee and fit the gears



Adjust the gib strip and we have a working knee.



This also shows the enlarged opening in the top surface of the knee to maximise the Y travel and fit in the larger ballnut.

This photo is the underside of the saddle casting with a shallow pocket about 1.5mm deep for the Y nut carrier



And the carrier and nut in place



Until the ball screw is fitted, it is vital that a tube is retained to stop the balls falling out hence the wire through the nut.

In order to fit the saddle on to the dovetails, the nut carrier had to be removed and then fitted up though the underside to the knee. Bit awkward but doable - thank heavens for ball ended allen keys!



And in with the ball screw




I have made a start on the X axis by fitting the screw into the nut and mounting it onto the top surface of the saddle.



This shows the X axis bearing carrier that bolts onto the table, I have bored this out to accept the nut flange which wins back another 12mm of table travel.

This shows the screw at the end of its travel.




I'm stuck now until some small socket cap screws arrive in the post - tomorrow?? These hold on a oil feed to the nut - there is just no room to use the intended oil port on the flange so I'm feeding oil in at the other end.

I'll show that in the next set of photos.

That's all for now folks!

Bob

[NickG]

Hi Bob,

Thanks for pointing this out, I'll be following along too now! 

Crikey, there's some work gone into this one too   


Looks great, keep up the good work.

Nick

[Rob.Wilson]

  dunt no how i missed your last couple of posts Bob 

Very nice  , I will make sure I keep an eye out in the new year for when you resume work on the mill 


Rob

[9fingers]

Rob, Something you might be interested in......

I wanted something to protect wiring and oil pipes across the moving section between slides and the static parts of the machine.

On the leesprings website I found tucked away in their tension spring section 'spring by the mile' well by the 3 foot length anyway.

I chose some made from just under 0.7mm wire and about 8mm bore/10mm OD and it looks the business. Minimum order is 5 lengths part no LEC026D-36-S  http://www.leespring.com/uk_product_spec.asp?partnum=LEC026D36S&springType=E&subType=
It is a tolerable screw in fit into m10 x 1.0 threaded hole to make terminations for it

There are various other sizes  - browse their extension spring catalogue around page 70 ish and scan though for free length of 12, 24 or 36" which make them stand out from the other springs.



In one place it says MOQ 10 off - elsewhere it is 5 off - I had no problems ordering on line for just 5 - I did have to wait a week or so for stock but it was worth it. I'm very pleased with them

Bob