What tool is needed to turn the face of disc wheels?

andrewnummelin
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What tool is needed to turn the face of disc wheels?

Postby andrewnummelin » Tue May 10, 2011 9:05 pm

Needing some disc wagon wheels that are smaller than any commercially available, I decided to have a go at turning one myself. Having very little experience with a lathe, I didn't expect this to be easy but I hit a problem I didn't expect.
I'm not expecting to turn any sort of dished profile, simply a flat disc recessed between the tyre/rim and hub would be OK.
For this I'm using a Unimat 3 and steel bar.

My first thoughts were to use standard tools and cut from the middle of the disc to the rim and then from the middle of the disc to the hub. This didn't work because the tool would not cut deep enough axially.

Second attempt was to try a standard steel parting off tool, but the cutting width was too wide. (It also would not function as a parting off tool as it failed to cut adequately.)
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Third go was with a carbide tipped "pointed" tool - this at least cut but cannot give the sharp edges between disc and rim or hub. (The tip is slightly rounded, not sharp - this tool was used to reduce the diameter of the bar to just over the flange diameter and cut beautifully.)
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The final "try" was with a parting off tool made of a blade clamped in a holder. Because the blade is higher than the stock it cannot be clamped in such a way as to come in the right position to do the job (the cross slide will not advance far enough).
(This tool also works very poorly at cutting off - it struggles to cut at all!)
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What I think I need is something a bit like a narrow cutting off tool that will cut on both sides. Am I right, and if so, does anyone know where I can get one? (Please don't suggest trying to grind my own - I have never had any success in grinding or sharpening tools, hence the acquisition of a set of carbide tipped ones.)

What did work was the bit where I expected problems! I turned the tyre profile roughly to size using the "pointed" carbide tool and then finished it off with a form tool. This chattered at the recommended cutting speed, but increasing the speed a notch gave a nice finish. Thanks Terry for giving me the encouragement to try it.
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Regards,

Andrew Nummelin

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Wizard of the Moor
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Re: What tool is needed to turn the face of disc wheels?

Postby Wizard of the Moor » Tue May 10, 2011 9:57 pm

Andrew,

Are you planning to drill the wheel for an axle, as opposed to leaving a stub axle formed from the bar stock?

If so, I would drill for the axle and use the resulting hole as clearance to get a standard knife tool started cutting from the center to the rim.

Nice job turning the tyres, BTW.

nigelcliffe
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Re: What tool is needed to turn the face of disc wheels?

Postby nigelcliffe » Wed May 11, 2011 7:26 am

Like the Wizard, I would consider drilling the axle before parting off.

If you parting tools are not able to do the job (some of mine have problems), then I would part off well behind the flange area, if necessary in a vice with a hack-saw. Then, I would mount the wheel with the back outwards and clean up the rear. Ideally I'd put the wheel in a collet chuck (I have them), but if you don't have one....

Three-jaw only solutions, there will be more than these three (pick the one you like!):
1 - For just facing the rear of the wheel, the concentricity of a collet isn't required. WIth a three-jaw, put a piece of shim around the wheel tread to protect it against damage from the three-jaw's pressing on the tread. Then close the chuck carefully onto the tread of the wheel. Turn only the rear face of the wheel, not any part of the rim/tread.
2 - Make a split tube collet for the three-jaw. A tube is turned up in the three jaw. Mark its position against no-1 jaw on the three-jaw (so it can go back in the same place, your chuck jaws should be numbered). Slit the tube lengthways with a fine saw. Clean up any burrs. When re-fitted in the three-jaw this is a collet.
3 - with a wheel which is bored for an axle, make up a stub-axle held in the three-jaw, with a wide face for the wheel front to rest against. Fix the wheel to the axle using shellac (wit back of wheel available to turn). Allow shellac to set, and turn the rear face of the wheel. Remove the wheel from stub axle by heating things to around 100C - shellac liquifies well below 100C, and any residue can be cleaned with meths. Shellac is available in crystals from the better wood work suppliers, dissolve the crystals in meths. I keep a small bottle with a good screw-top lid ready dissolved.


- Nigel

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Tim V
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Re: What tool is needed to turn the face of disc wheels?

Postby Tim V » Wed May 11, 2011 4:26 pm

I expect it's very satisfying making your own wheels. However, none of your tools look sharp, especially that final picture of the parting tool. The edges are rounded. You must have sharp tools on small lathes, sharp enough to cut your finger is the rule!

I have bought diamond hones in the Pound shop which are good enough.
Tim V

andrewnummelin
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Re: What tool is needed to turn the face of disc wheels?

Postby andrewnummelin » Wed May 11, 2011 9:31 pm

Guys,
Many thanks for the rapid responses and encouragement.

Wizard,
I'd not really thought about a stub axle..... could be of value in a future project.
I don't think starting with a knife tool in a drilled a axle hole would work as this would remove the boss. (One could I guess drill the hub diameter, cut the disc with the knife tool, epoxy in some tufnol or similar to form an insulating hub and then drill this for the axle.)

Nigel,
Thanks for the suggestion for doing the back of the wheels, a couple I'd not hear of before.

Tim,
I'm sure you are right about the last photo - I've tried a few times to sharpen it but my lack of skill is clearly apparent! Any hints on how to do it?
But the tool in the first shot (blue painted) is new and I would assume to be sharp: the second carbide tipped tool has a slightly rounded tip, pretty close to the flange root radius, and cuts extremely well.

-------------------------

Following a trawl through old magazine cuttings remembered some reports on the production of spoked driving wheels based on making a tyre separately from the spoke and hub and this made me wonder whether it wouldn't be easier to do the same with the wheels I need. Turn the hub and disc from brass and make the tyre from steel - I wonder what the largest drill is that the Unimat could deal with before using a boring tool to make a tube. Would it better to bore out the centre then cut the tread profile, or cut the tread first and then bore out the middle?

Any comments or suggestions would be more than welcome.
Regards,

Andrew Nummelin

nigelcliffe
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Re: What tool is needed to turn the face of disc wheels?

Postby nigelcliffe » Wed May 11, 2011 9:58 pm

Tools and tool sharpness; there are any number of lathe text books around; the one which is sold with Cowell's 90's might be suitable for a Unimat owner (a Cowell 90 being only a little bigger than a Unimat, though the Cowell is much more rigid).

A few things though;
In general carbide tools are designed for rapid rotating production machines taking massive cuts in one hit. You can't do this with a Unimat (or my Cowell!) as the motor isn't powerful enough and the machine not rigid enough to withstand the forces. I do have some carbide tools for the Cowell, they work, but finish is much better with other tool materials...

My better tools are made from high speed steel, which can be either ground from rectangular blanks (I have some which are 1/8th square in small holders), or can be made from old round drill shanks if you have a suitable holder for round bodied tools.
I make most of my smaller lathe tools using a grinding disk in a mini-drill to grind it to shape. Very occaisionally I use a 6 inch bench grinder, but that is rare. I finish tools with either a hand held stone or a hand held diamond hone (these are very cheap nowadays). Some tools have a sharp plan profile, others curved; it depends on their purpose (read a text book or two...). Hardly any of my tools have any top-rake, I don't find it necessary with very small tools and small diameters, though there is front and side rake.


And, whilst not that useful for wheels, don't dismiss hand turning as an option - see the first part of the article on the "Fonly" lathe which is referenced from the 2mm Scale Association website for a neat hand turning toolpost. A similar design can be constructed to use on the Unimat (and I have one for my Cowell). And the fully hand turning option with a graver (as used on many clock-making lathes), optionally held against a rest, can be very useful.


- Nigel

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Tim V
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Re: What tool is needed to turn the face of disc wheels?

Postby Tim V » Thu May 12, 2011 6:17 pm

andrewnummelin wrote:Guys,
Following a trawl through old magazine cuttings remembered some reports on the production of spoked driving wheels based on making a tyre separately from the spoke and hub and this made me wonder whether it wouldn't be easier to do the same with the wheels I need. Turn the hub and disc from brass and make the tyre from steel - I wonder what the largest drill is that the Unimat could deal with before using a boring tool to make a tube. Would it better to bore out the centre then cut the tread profile, or cut the tread first and then bore out the middle?

Any comments or suggestions would be more than welcome.


There was an article by Sid Stubbs in a MRJ which was a rewrite of his seminal articles in the June '59 MRN. I've used a similar form tool to get the wheel profile on a Unimat.

I would suggest that you need to look at how firmly you can hold your material. A four jaw chuck will hold items more firmly that a three jaw. A collet would be even better. If you go down the hand turning route as suggested by Nigel, you would need to get away from chucks, they can make a mess of knuckles.

The forces involved can be substantial. Suggest form profile, then bore out the middle. Don't forget there are many types of steel, some more free cutting than others, I remember one I had cut like butter!

I can add no more than Nigel has regarding sharpening.
Tim V

nigelcliffe
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Re: What tool is needed to turn the face of disc wheels?

Postby nigelcliffe » Thu May 12, 2011 6:40 pm

Tim V wrote:I would suggest that you need to look at how firmly you can hold your material. A four jaw chuck will hold items more firmly that a three jaw.

Though most 4-jaws are "independent", so setting work to be centred is a lot of work, and the quick diy split collet doesn't work easily with them.

If you go down the hand turning route as suggested by Nigel, you would need to get away from chucks, they can make a mess of knuckles.


YES, this is IMPORTANT, sorry, I forgot to mention it earlier. If hand-turning, you need at least a full shroud around the chuck, and ideally something with a properly smooth exterior, such as a collet system.

I think collets for the Unimat, using ER11 or ER16 types, can be assembled fairly cheaply; full sets of ER collets from the likes of Axminster, Arc Eurotrade and J&L Supplies can often be cheap.


.............Don't forget there are many types of steel, some more free cutting than others, I remember one I had cut like butter!


The better steel suppliers can give a specification number for the steel bar. Its worth paying extra for decent quality material.


- Nigel

Terry Bendall
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Re: What tool is needed to turn the face of disc wheels?

Postby Terry Bendall » Fri May 13, 2011 4:40 pm

Rather a late contribution to this thread but it may be useful.

Parting off if one of the more difficult jobs in lathe work both in the size of work that we do and in the work done by live steam model engineers. My parting tool is shown on page 33 of Scalefour News 166. It measures 9mm x 2mm in cross section and is in fact a blade intended for a larger parting tool holder. You can just see in the picture some of the packing needed to maintain it in the correct position.

Parting off on small lathes always works better if the tool is mounted upside down in a rear tool post as shown in the picture. i have no idea if such a tool post is made for the Unimat or even if one can be fitted but if you can get one and it will fit, this is the way to go. Use a slow speed and on steel plenty of cutting oil. As others have said the tool must be sharp, and a small oilstone or diamond slip stone will improve things no end.

Another point is that the end of the parting tool should have a small radius ground in it. The drawing on page 9 of Scalefour News 156 did not come out very well - my fault in using too fine a line setting on the CAD package, but the radius can just be seen and this helps the tool to cut much better. The book I recommended - The Amateur's Lathe by L.H> Sparey is the best that I found for information on cutting tools and I have been using the shapes and angles recommended in the book for 45 years on lathes of many different sizes including large ones. The book is still available - details on page 19 of 155.

The Sid Stubbs series of article on making wheels are on the web site of the Manchester MRS.


Terry Bendall

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John Bateson
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Re: What tool is needed to turn the face of disc wheels?

Postby John Bateson » Fri May 13, 2011 4:53 pm

The Amateur's Lathe by L.H. Sparey
Lost hope waiting for the library to get one for me, so got it from Amazon for about a fiver. Excellent book, if some of the machinery is a little ancient. Has been reprinted 5 times since 2002.

Parting off - I hate it. I have been working on a smoke box door and just could not get the back of it flat using any parting off tool so it wouldn't fit properly in the smoke box. There was an obvious solution but it took me 7 tries to get there. I would expect a similar problem with wheels.

John
Slaving away still on GCR stuff ...
Avoiding the soaps ...
http://www.greatcentralmodels.co.uk

andrewnummelin
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Re: What tool is needed to turn the face of disc wheels?

Postby andrewnummelin » Fri May 13, 2011 6:44 pm

Gents,
As always on this Forum there's loads of help offered: many thanks to you all.

I'll now have to go shopping, (re-)reading, practising, ... at least some of this can be done while remaining in an armchair!
Regards,

Andrew Nummelin

David Knight
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Re: What tool is needed to turn the face of disc wheels?

Postby David Knight » Fri May 13, 2011 8:33 pm

Another belated addition to the reference library ;)
Sharpening Small Tools, Ian Bradley, MAP/Argus Books Ltd.
ISBN 0 85242 459 0 covers a multitude of tools even including drawing instruments. Lathe tools are well covered.

HTH

David

Terry Bendall
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Re: What tool is needed to turn the face of disc wheels?

Postby Terry Bendall » Mon May 16, 2011 6:35 am

John Bateson wrote:Parting off - I hate it. I have been working on a smoke box door and just could not get the back of it flat using any parting off tool so it wouldn't fit properly in the smoke box. There was an obvious solution but it took me 7 tries to get there. I would expect a similar problem with wheels.


One solution is to grind the front of the tool at a slight angle so the the corner reaches the centre of the workpiece side of the bar. However the forces involved often means that the work shears off at the middle, rather than being cut which will leave a small pip. Taking two cuts as suggested in part 9 of the Machine Tools series will help. To remove the pip the solution is to hold the work with the parted off face outwards and take a facing cut. The difficulty then of course is to hold the work "square" in the chuck so that it turns without wobbling. This can be done using a home made split collet which has a recess turned in it to take the work. For something like a smokebox door the recess whould need to be roughly shaped at the bottom to allow the door to be held. To make the collet I would use a piece of metal - brass may be better to hold brass items to avoid marking the firnished work, but steel would do, and make it about 12mm long so that it will run in the chuck without a wobble. An even better way would be a set of stepped collets. Such things do exist but I would guess difficult to find as new items.

John Bateson wrote:Has been reprinted 5 times since 2002.


Good to see that the book can still be found. I bought my copy in 1965 which was the fourth edition. The first edition was published in 1948.

Terry Bendall

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Tim V
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Re: What tool is needed to turn the face of disc wheels?

Postby Tim V » Mon May 16, 2011 12:55 pm

One thing that came up in conversation yesterday is that information for "small lathe" users is scattered here and there. Even Terry suggests a back parting off tool holder. Small lathes don't have such things. The books that have been written for model engineers refer to small as - a Myford!

There is a wealth of knowledge out there, but it's getting it into one place.

Anyone up for the challenge?
Tim V

nigelcliffe
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Re: What tool is needed to turn the face of disc wheels?

Postby nigelcliffe » Mon May 16, 2011 5:19 pm

Tim V wrote:One thing that came up in conversation yesterday is that information for "small lathe" users is scattered here and there. Even Terry suggests a back parting off tool holder. Small lathes don't have such things.


Yes they do !
My Cowell ME90 has one, the rear toolpost is still listed on Cowell's website pricelist.


There is a wealth of knowledge out there, but it's getting it into one place.

Anyone up for the challenge?


I agree its needed, but I'll not be compiling it, too many other things to do !

- Nigel

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Tim V
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Re: What tool is needed to turn the face of disc wheels?

Postby Tim V » Mon May 16, 2011 6:46 pm

There's always one of the lathes that has one!

Anyway here is my parting off tool, ground the way I was taught a long time ago. Crucially, this tool will face the back of the item off, and leave the pip on the waste (which is on the left). A difficult item for the camera to focus on.
IMG_1270.JPG
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Tim V

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Wizard of the Moor
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Re: What tool is needed to turn the face of disc wheels?

Postby Wizard of the Moor » Mon May 16, 2011 10:11 pm

Terry Bendall wrote:An even better way would be a set of stepped collets. Such things do exist but I would guess difficult to find as new items.

One alternative is to use a chuck with a set of soft full-circle jaws.

Close the jaws up on a small bit of bar to hold them tight. Then turn a shallow recess into the jaws that will hold your wheels, either by the tread or the rim.

When you remove the bar and close the jaws on your wheel then it will be held securely and concentrically. You can then skim them to width, cut a recess into the spokes, form a disc profile or whatever.

With careful planning, one set of jaws can be machined to hold several diameters of wheels in different depths of recesses. Always tighten the jaws before machining a new recess to ensure that it will be concentric for that wheel diameter!

Of course, you have to buy a lathe that offers this kind of chuck as a standard accessory

It also has a T-bar section rear-mounted parting off tool available. Nice!

No connection, just a satisfied metal mangler, etc.

Terry Bendall
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Re: What tool is needed to turn the face of disc wheels?

Postby Terry Bendall » Tue May 17, 2011 6:31 am

Wizard of the Moor wrote:Of course, you have to buy a lathe that offers this kind of chuck as a standard accessory


Having had a look at the Petol site, the lathe and the accessories look good. Petol lathes have been around for a long time and I had forgotten about them when i wrote the articles.

Tim V wrote:There is a wealth of knowledge out there, but it's getting it into one place.

Anyone up for the challenge?


Funny you should say that Tim. Both Chairman Jim and former Editor John thought there was some milage in a book about machine tools for the modeller, using the material that has appeared in Scalefour News and expending on it. It may well happen as a Society publication but at the moment I have too many other things on. There are also serveral other Society piublications in the pipeline. However I am not precious about the subject so if Someone else wants to put something together I would be prepared to assist.

Terry Bendall


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