Author Topic: Smart and Brown Lathe Crosslide Screw Renewal  (Read 25696 times)

Offline Darren

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Smart and Brown Lathe Crosslide Screw Renewal
« on: November 21, 2008, 05:22:16 PM »
Another new project for me,

I guess some of you remember me whittling on about my worn crosslide screw on my S&B lathe.

In case you forgot, it looks like this, a little past it's best   :bugeye:



Well I decided to do something about it and purchased a 1M length of 10mm x 2mm pitch Trapezoidal Spindle and a matching tap for cutting the nuts to go with it.
I did consider cutting my own screw thread on the mini lathe, but decided that a it might be a bit ambitious for me at the mo and a proper rolled thread would not only be finished better but last much longer as well.
The original thread on the lathe was 3/8 Acme at 8tpi. I decided to convert to metric for no other reason than I understand it better than imperial. My dials have 100 graduations so no probs there.



Commonly known around these parts as a "Crap-o-CAD"



This is a piece of 20mm 303 SS bar, soon to be the "handle" end of the screw.



Drilled and tapped 8mm 1.25 pitch



Now the screw thread, turned down and threaded 8mm 1.25 pitch to match



Viola.... they fit, not that difficult so far...:thumbup: 



A little bit more work and



As you can see I have made it 2" longer, the slide can take it and I hazard it may come in useful sometime. This lathe originally has a long crosslide but a short screw? not any more it doesn't !!

I still yet have to decide how to fix the threaded section into the "handle" end, locktight, cross pin or braze, maybe just solder will do? Any suggestions chaps?

Also the 3/8 thread needs doing for the slop adjusters, but that will have to wait for the mini lathe to return from the Doc's. Be the first job it'll do.  :dremel:

Well, I hope someone found that interesting.... :D

Darren

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Offline Brass_Machine

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #1 on: November 21, 2008, 05:33:36 PM »
Nice start Darren.

Keep the pictures coming!

Eric
Science is fun.

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Offline John Stevenson

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #2 on: November 21, 2008, 06:07:10 PM »
Why didn't you saw the old end off the knackered screw and stub it into the end of the new thread ?

John S.
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #3 on: November 21, 2008, 06:20:16 PM »
I did think of that,

But I needed the old one to make the new one, would have been a bit difficult without it.... :thumbup:

Apart from that, the old one has some over sized clearances which I intend to tighten slightly.

Darren

PS, I could have done simply cos other the other tooling I have with this lathe, but, but....do I need an excuse,  :med:
« Last Edit: November 21, 2008, 06:23:21 PM by Darren »
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bogstandard

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #4 on: November 21, 2008, 08:07:10 PM »
Darren,

Go the way of belt and braces, cross pin after assembly with a touch of loctite.

No need for anything spectacular.

Measure up a nail (of the hammer it home type), drill hole to same size, put nail thru with a dab of loctite, trim off a bit longer than needed, then wack nail until it swells in hole, clean off the hammered end bits, et voila, one solid fixed end, and if anything untowards happens, the soft pin will shear, without hopefully, any damage to the threads.

You have to read it all in one breath

John

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #5 on: November 22, 2008, 08:40:05 AM »
Carry on with this one Darren,

Sooner or later some of us will be doing similar to our machines.... It's always good to have a reference article to browse to help you on your way  :thumbup:



Ralph.
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #6 on: November 22, 2008, 08:46:38 AM »
Thanks guys, I will continue later...

One thing I forgot to mention was the the "handle" end was machined to size after fitting it to the thread buy holding the threaded section in a lathe collet.

This should make it true to the thread.. :D.

Next job it to make the nuts, thinking of what material to try here....back later... :headbang:
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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #7 on: November 22, 2008, 09:22:23 AM »
Darren,

The accepted material for the nuts is bronze (PB1), if you try brass, I think you will find it will wear very quickly. Steel is definitely a no-no, the nut and screw are liable to gall and friction weld together.

John

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #8 on: November 22, 2008, 11:09:13 AM »
Opps, bit of underlining there...!!

I have some PB1 for one nut but not big enough dia for the other (I could get some of course), but I was thinking of trying Delrin or Teflon both of which I have.

I thought it might be interesting to give them a go?

Darren
« Last Edit: November 22, 2008, 11:23:00 AM by Darren »
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bogstandard

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #9 on: November 22, 2008, 11:23:13 AM »
Darren,

You have to remember, the lead screw and nut is not just for positioning, they take the full force of the cutting action. The metal is pushing against the two parts because it doesn't want to be cut, you are forcing the cutting tool into the metal.

That is why you have all your correct cutting angles and clearances, it helps to take the pressure off the cut, so the machine doesn't have to work too hard.

You can try it, and prove me wrong, but I suspect you will start to have trouble almost straight away with the finish, as the tool bounces backwards and forwards because of the flexibility of the nut. You could eliminate the pressure on the nut by tightening the jib lock before starting the cut, but that is not an ideal situation.

John

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #10 on: November 22, 2008, 11:42:46 AM »
Good point John, Teflon deff out then, I read somewhere that it's neither a true solid or liquid, something in between, like glass.

But you could have a point with Delrin as well...umm... :thumbup:
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Offline CrewCab

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #11 on: November 22, 2008, 11:46:32 AM »
Opps, bit of underlining there...!!

You can always nip back in and edit your post Darren

Phosphor bronze has been used for this sort of application almost since the stone age, and for good reason I suspect. ........... I used Delrin for the cylinder of a tiny model engine and whilst it ran well enough the thread for the securing bolt didn't last too long.

CC
« Last Edit: November 22, 2008, 12:12:52 PM by CrewCab »

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #12 on: November 22, 2008, 06:42:42 PM »

Thanks, I was just thinking of experimenting just to see and learn really.
Anyway, for tonight I cut one of the nuts, from PB1 btw

Started with a piece of scrap that I'd been playing with recently



Turned it down to size and threaded it, thought I'd taken a pic but it seems not.... :hammer:

It needed a retaining slot to stop it spinning, I'm a little low on milling cutters and didn't have one small enough (some on the way in the post)
So I decided to give this a go in the lathe. It's a HHS parting tool on its side.



Not the neatest job I'll admit, Had to take very light cuts and take it real slow.....but it seemed to have worked.



It even fits the thread too, handy that...... :D Feels nice and smooth as well, the original screw was kinda rough.



Well that's it for tonight, a bit further on. Now I need to order some 35mm PB1 for the other nut....

Darren



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bogstandard

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #13 on: November 23, 2008, 12:38:19 AM »
Darren,

That is looking real well.

I see you are discovering methods all by yourself. Cutting the one off side groove on a lathe is almost exactly how it is normally done.

I see we have a natural machinist coming along here.

John

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #14 on: November 23, 2008, 05:17:03 AM »
"almost" feel free to educate me  :D

I seem to remember seeing it somewhere cutting internally, broaching I think it was called? Possibly cutting a gear.
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Offline John Stevenson

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #15 on: November 23, 2008, 06:53:25 AM »
What about using the phossie nut you have made and then using a Delrin nut spaced out from the phossie one with those dished washers.
That will provide zero backlash without relying solely on a soft Delrin nut.
You can make spare up at the same time for replacements down the line.

The dished washers will keep a preload on the whole shebang.

Just guessing here as i don't know the build up on a Smart and Brown lathe

John S.
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #16 on: November 23, 2008, 02:01:25 PM »
Hi John, interesting idea, but not sure it will work in this case due to the design of the machine.

Thanks
Darren
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #17 on: June 27, 2009, 05:07:07 PM »
Wow, this one had to have the cobwebs blown off..... :lol:

Well a little more progress today, first to make the backlash nuts shown in this picture from the SS bar end below the two nuts.



Roughed out with and old tip in the funny orientation holder to use the "other two" cutting edges.



Final shape with a new tip. I'm just putting a groove in for the friction spring that tensions the indicator dial.



Drilled,counter drilled part way and tapped 8mmx1.25.
The original was 3/8 with a 20tpi thread. 20tpi is almost 1.25mm metric pitch, so I chose an 8mm thread as the pitch was more important than the diameter...



I also threaded the leadscrew 8mm at the handle end by single pointing on the mini lathe as i don't have an 8mm die. Sorry forgot to take pictures of this  :doh:


Set up in a 5C collet fixture to drill a 3mm hole for the locking pin of these two parts.



Counter sunk with a 6mm spotting drill and then turned a 3mm brass pin. I chose brass in case I ever wanted to take it apart. Easier to drill a soft brass pin out than a hard steel one.
Also brass would be easier to beat into the countersunk areas to secure it.





Now beaten into place. The pin should also swell inside the hole to make a nice tight fitting.



This is how it all fits together. You can see the old two backlash adj nuts in the bottom of the picture. They have holes in them to insert a bar to open and close them for adjustment.
Firstly they can be rather tight, and with a small bar (drill bit) it can be very difficult to undo them. Secondly the drill bits usually bend  :doh:
Thirdly the holes become distorted in time making them useless....

So what to do? Mill two flats for a spanner fitting, drill similar holes but make a pair of proper bars, say a short 4mm diameter to fit the nuts and then expand to 6mm or more. Would be easier to use than drill bit  :ddb:

Or something else, any suggestions welcome...







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Offline John Stevenson

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #18 on: June 27, 2009, 05:22:54 PM »
Slots and a C spanner ?

John S.
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #19 on: June 28, 2009, 06:53:05 AM »
Thanks John, I did consider that but the thought of making a c-spanner has put me off. I'll prob go for simple holes but make a proper fitting pair of keys/bars. Should cause less damage that way I think.

Indecently, I recently bought a Drill Doctor drill sharpener and this is the first real chance I have had to test the results. I'm happy to report that the sharpened bits drill better than some new ones I have, seem smoother. But the split points that this unit is capable of producing is a real eye opener. You can push a 10mm bit through a SS bar as if it was a 5mm bit with no smaller counter bore hole or center drill first.
I'm really impressed with the sharpening results.

I have re-sharpened about 200 drill bits so far so I consider it already paid for. Also I sharpened some snapped drill bits to make some stub drills to benefit from the extra rigidity.

A tool worth having IMHO....
« Last Edit: June 28, 2009, 07:28:51 AM by Darren »
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #20 on: June 29, 2009, 05:38:20 PM »
The next part to this saga is one I have been agonising over for months. I just didn't have a piece of leaded bronze big enough.... :bang:

For months I have been watching Ebay for a piece, but nothing has come up. New prices, well you just don't want to know....
I needed a 2" round and when they get to that size it just gets silly for making a simple nut.....!!


I have spent 6hrs today polishing my new concrete garage floor that was laid yesterday. That's on your hands and knees floating 24hr old cement. Floating, wetting, floating, wetting and polishing in an effort to get a smooth floor ready for painting when it has fully dried.

Anyway, some sanctuary in the workshop was called for, alone where it's quiet  :lol:

Then it struck me, I already had the material for this nut, I was just looking at it the wrong way.

I bet I've lost you all by now so better show a pic of what I'm on about.... :ddb:

This is what I want to make from this bar, but the dia is too small



But if we look at it this way on....



On the miller to machine a flat, I need somewhere to calculate from, a datum if you like



Turned it over to machine the other side flat, carefull not to take too much off



Center punched the position for the threaded spigot, and set up off center on the lathe in the four jaw chuck



Don't brass chippings just love to fly everywhere at great speed. Here's my patented brass chipping barrier  :lol: An old shop leaflet display re-shaped and help down with a microwave magnet.... :dremel:



Spigot now turned



Threaded with a trapezoidal tap, 10mmx2 pitch



Trimmed to length, note a tiny pip of the original bar curvature, couldn't be helped as there had to be compromises due to material size



Out of the four jaw, turned around and into a collet



I forgot to take the next pic, sorry, I simply rounded off the backplate a bit to size

Back on the miller in a collet fixture to machine two flats



And voila.....!!
The flat on the bottom is of no consequence, another compromise, but not an issue.





All that's now needed is two curved slots.....gulp.... ::)

That means the rotary table that I've yet to figure out how it works and how to mount this piece. I'm thinking MT2 blank end drilled and tapped to hold this nut?









« Last Edit: June 29, 2009, 05:47:04 PM by Darren »
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bogstandard

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #21 on: June 29, 2009, 05:57:52 PM »
Wonderful stuff Darren.

You are starting to look at pieces of metal how they should be looked at in our game. Forget what shape the original metal is, imagine the piece you want being in there. Then using your ingenuity to make it come out.

Now you have to take the plunge Darren, and get the RT set up. This just might be the push you need to get you working in another dimension. A rather different and sometimes difficult learning curve, but once you get the hang of it, you will wonder how you ever made things without it.

John

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #22 on: June 29, 2009, 06:47:56 PM »
Thanks John,

I was quite pleased with myself today. Firstly I was just sitting there having a coffee and a smoke, as you do in your own little space, when it struck me.
Secondly cos it worked out quite well.

Next moment I get I'll set up the RT and have another "ponder" on how to proceed...
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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #23 on: June 29, 2009, 08:07:41 PM »
Top job  :thumbup:

It'll certainly do it's intended job   :beer:



I think your RT set up idea sounds about right..... As I see it all you need is a slot drill of the right size (usually 2 flute) to make it a little easier!




You'll figure it out no worries Darren  :smart:





Ralph.
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Offline sbwhart

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #24 on: June 30, 2009, 02:09:18 AM »
Nice Job Darren well done  :clap: :clap: :clap: :clap:

You'll have no problems with the RT, the M2 tapered mandrel is the way to go, I've used a similar technique myselve a number of times.
 
:nrocks:

Have fun

Stew

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Offline Stilldrillin

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #25 on: June 30, 2009, 02:27:02 AM »
That will do nicely Darren.....  :clap: :clap:  :thumbup:

David D
David.

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Still modifying bits of metal... Occasionally, making an improvement!

Offline CrewCab

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #26 on: June 30, 2009, 07:34:20 PM »
Nice one Darren .......... impressed2  :thumbup:

as for the concrete .............



just a thought     :coffee: ........... I know it's more expensive but it's but far less stressful on the knees mate

CC

Offline John Hill

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #27 on: June 30, 2009, 07:39:28 PM »
CC, too right, those concrete helicopters are wonderful machines.  In the hands of someone who knows what they are doing they can produce an almost gloss surface which seems to have high resistance to oil staining.
From the den of The Artful Bodger

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #28 on: June 30, 2009, 08:14:58 PM »
John, you ain't wrong mate, my knees are suffering, wet cement ain't too kind to skin.  :thumbup:

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Offline John Hill

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #29 on: June 30, 2009, 09:30:58 PM »
Darren, wet cement is caustic and best kept off your skin if you dont want housmaids' knees and hands!

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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #30 on: July 02, 2009, 06:53:47 PM »
Now that I have my rotary table set up and ready to use it's time to cut some curved slots in the anti backlash nut.... :ddb:

Not having used a rotary table before this fool set up a dial gauge in the mill spindle to center the RT....you wouldn't credit it would you?
When I realised what I was doing I felt so dumb...!!! :scratch:

If the work is correctly centred on the RT then that's it, cos the RT is used "off center" cos that's what it's for  :doh:

Anyways, there was no need for any real precise work here so the area to be cut was marked off with a pen by spotting through the old nut.



Four holes were drilled to help the milling cutter out a little.



Then it was milled with no drama or anyfink..... :ddb:



Job done



Well that wasn't very exciting, maybe the next bit will be, can only hope eh?

Sum of parts made so far



Now to the fitting of these parts to the lathe. The two nuts needed to tighten together whilst at the same time they both ended up in the correct orientation. Otherwise there would be no point in having them at all.....bit like the originals, prob not original cos they were way out in this respect.

Either one of the two nuts needed to be faced/shortened until they met as described above, I chose the round one cos it's a darn site easier to do than the other one...  :smart:



Now fitted, the round nut is just ahead of this one just inside the slide. It's held from turning with a small keyway shown earlier in this thread.



The two nuts meet together with the outer nut in the position shown above. As things wear the outer nut is turned clockwise to take up any slack. As you can see I have set it so that I can gain maximum adjustments over time....

Next to finish the other two locking SS nuts off and we should be almost done..... :)

« Last Edit: July 02, 2009, 07:04:43 PM by Darren »
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Offline Stilldrillin

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #31 on: July 03, 2009, 04:11:08 AM »
VERY nicely done Darren!  :clap:

Not having used a rotary table before this fool set up a dial gauge in the mill spindle to center the RT....you wouldn't credit it would you?
When I realised what I was doing I felt so dumb...!!! :scratch:
If the work is correctly centred on the RT then that's it, cos the RT is used "off center" cos that's what it's for  :doh:

Not the least bit dumb!  :wave:

You should always know where the centre of the r/t is, so you can pace out from that datum point for your hole positioning etc.......  :thumbup:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #32 on: July 03, 2009, 04:16:34 AM »
Gotcha.... :thumbup:

Now I need to work out how to find the centre of the RT cos what I was doing last night would never have found it. But it did prove that the spigot I made was truly centred on the RT itself.

Mind you, I'd have been a bit worried if it wasn't......
« Last Edit: July 03, 2009, 04:18:35 AM by Darren »
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Offline Stilldrillin

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #33 on: July 03, 2009, 04:23:32 AM »
Gotcha.... :thumbup:

Now I need to work out how to find the centre of the RT cos what I was doing last night would never have found it. But it did prove that the spigot I made was truly centred on the RT itself.

Mind you, I'd have been a bit worried if it wasn't......

Hold finger clock in spindle.

Rotate, to clock bore or centre spud of r/t.  :thumbup:
« Last Edit: July 04, 2009, 02:02:18 AM by Stilldrillin »
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

bogstandard

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #34 on: July 03, 2009, 09:55:10 AM »
Darren,

Just to give you a litle tip.

It is not always necessary to centre the RT or the job.

Say you want to drill 12 equidistant holes around a plate and you already have a centre hole in the plate, and you are not after perfect thou accuracy. Just mark on the plate where the first hole is to go, mount the plate into the RT centre using whatever is necessary, a bolt held in the chuck is favourite. Then just position the marked hole under you cutting bit and drill away, then just rotate the RT by the number of degrees required, and drill another hole. As long as the centre of the job is on the same centre as the RT, and you have placed the position to be drilled under the cutter, then every hole after that will be on the same PCD as the first. No need to centre the RT.

The job you have just done would be a good example of use of that method.


Bogs

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #35 on: July 03, 2009, 11:35:19 AM »
Thanks John, that's pretty much how I did it this time.

There's nothing like practical exp, I'm sure it will all become much clearer as time goes on... :thumbup:
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Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #36 on: July 03, 2009, 03:31:31 PM »
Stuck the two nuts in a hex collet holder and drilled six 3.5mm holes in each. Next job to make some small Tommy Bars....is that the right name?



Back on the lathe, a little stiff at first but soon freed up with a couple of turns backwards and forwards.




I now have a half metric lathe that will be much easier for me to get on with  :ddb: :ddb: :ddb:

Oh, and got rid of some slop of course. Now have to let it bed in and see how it goes.....
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Stilldrillin

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #37 on: July 04, 2009, 01:58:06 AM »
Darren,
Those are 2 sweet looking locknuts.....  :thumbup:

That machine`s looking good inside & out!  :clap:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Darren

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Re: Smart and Brown Lathe Crosslide Screw Renewal
« Reply #38 on: July 04, 2009, 05:24:15 AM »
Thanks David,

If I'm honest the cross slide unit is a bit rough all round. Someone has also chewed it quite a bit at one end with a hacksaw by parting off work. The cross leadscrew ( Y?) was badly worn, hence I renewed it.

But it cuts straight and leaves a good finish despite it's roughness.

Fortunately the cross slide and tailstock came from another machine and I just added them to my sliding turret and lever cross slide tooling to give me more options.
The rest of the lathe is in fairly good condition.

I have found that since I actually started to use the dials on the mini lathe to gauge the depth of cut I was getting better results. I like to work in metric but couldn't really get on with the imperial dials of the Smart and Brown. So now hopefully I will find it a little easier to use with the metric screw conversion.

We shall see....fingers crossed there will be an improvement..... :dremel:
« Last Edit: July 04, 2009, 05:30:42 AM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)