Loco wheel profile chatter

[LukerParticipant @luker]

Hi everyone,

I have a question for the loco making guru’s. Whenever I machine the profile of the wheel I get chatter on the inner flange. Basically I machine a “square form” on all the wheels using a mandrel, then with a carbide (ground) tip, silver soldered to a dedicated holder I plunge to form the flange and finish off the taper using the taper slide. I machine in this fashion so that I can zero the lathe and cut all the wheels identically, and it’s much faster. The chatter only happens in the second I move from the top slide to the taper slide. I get the same with EN8 tires or from a profile machined directly to a casting.

Is there a trick I’m missing?

[LukerParticipant @luker]

[Michael GilliganParticipant @michaelgilligan61133]

I certainly don’t qualify for your target ‘Advisory Panel’ … but I do know a bit about vibration.

Mounting the wheel like that is inviting problems : It looks far too much like a cymbal.

MichaelG.

.

Ref. https://scholarship.rollins.edu/cgi/viewcontent.cgi?article=1020&context=stud_fac

Edited By Michael Gilligan on 02/04/2021 11:23:29

[duncan webster 1Participant @duncanwebster1]

I wouldn't do it like that! I'd get a disc about 6mm smaller than the finished OD of the wheels, mount a spike the same diameter as the axles in the middle. Make this spike longer than needed, then some tapped holes so you can bolt the wheels on through the spokes. Bolt wheel to disc, set up in 4 jaw using excess length of spike as datum and tapping wheel back against jaws then away you go.

If starting from blob I'd just machine the back of the wheel, not the centre hole, bolt wheels on and machine rim and hole at same setting

[LukerParticipant @luker]

Hi Guys,

Thanks for the feedback; you’ve given me a few things to think about. Michael, I liked the article, thanks for the link. I can’t say I know much about vibration; it has been a while since I’ve done a modal analysis, but I personally think the problem lies on the tool side. Sorry I should have elaborated a little more in the initial post. I have had the same result with spoke’d and solid wheels, with different materials so this should have shifted the modal point, but the intervals between the chatter ‘marks’ were identical. This makes me think the problem is on the tool side.

Thanks Duncan, next time I’ll have a look at a wheel turning setup like you’ve described. How many wheels have you machined using this method?

The greats like LBSC and Martin Evans used to machine their wheels using mandrels?

[Phil H1Participant @philh196021]

Luker,

I machine wheels using a face plate method not dissimilar to the method described by Duncan. I have machined a few directly onto the face plate to get the hole straight and in the middle.

I have read both the M Evans and LBSC descriptions and I don't like the bit about boring the hole from the back but they always seem to describe a faceplate (usually and old unused locomotive wheel) for machining the tread. I have seen a mandrel mentioned but I didn't like the look of it because it seems flimsy.

I have never suffered with any chatter using the faceplate method. I haven't machined a huge number of wheels – about 25 to date.

Phil H

[SillyOldDufferModerator @sillyoldduffer]

Can you publish a picture of the tool in the lathe please Luker?

Looks like a vibration problem, and although Michael's cymbal is a credible suspect, tool shape and overhang may be making it worse. Vibration is a funny animal, not always obvious what the cause or mode is. That it vibrates at a particular point must be a clue, but I can't visualise what the cutter looks like.

Rubbing rather than cutting maybe, and that can be due to bluntness, incorrect rake and/or relief. The cutter may be scraping like a horse-hair bow across a violin string simply because the geometry isn't quite right. I'm guessing!

Dave

[LukerParticipant @luker]

Hi Phil,

Yep I’m going to give the faceplate a bash again; my Stirling single wheels were machined like that, but they were very large wheels with two taper slide setups so can’t really compare. I swopped over to the mandrel method with the last two loco’s I made because they had solid wheels, so a drive pin was not possible unless I deviated from the original. One positive about the mandrel method is that’s its very quick. The last loco had 12 smaller wheels that were completed in a Sat morning.

I was hoping for a “trick” that I had missed, but I will definitely machine a wheel on a faceplate to compare.

[LukerParticipant @luker]

Posted by SillyOldDuffer on 02/04/2021 17:30:24:

Can you publish a picture of the tool in the lathe please Luker?

Looks like a vibration problem, and although Michael's cymbal is a credible suspect, tool shape and overhang may be making it worse. Vibration is a funny animal, not always obvious what the cause or mode is. That it vibrates at a particular point must be a clue, but I can't visualise what the cutter looks like.

Rubbing rather than cutting maybe, and that can be due to bluntness, incorrect rake and/or relief. The cutter may be scraping like a horse-hair bow across a violin string simply because the geometry isn't quite right. I'm guessing!

Dave

The lathe has another setup in at the moment, but here's the tool. I try to keep the overhang as small as possible, not more than tool thickness, in this case 12mm. Rake and relief is ground for CI but I machine the EN8 tires with this tool as well. It gets ground between wheels sets, that's why it looks freshly ground. I've just finished a wheel set.

Your descriptive words for vibration are brilliant! Please can I use paraphrase and recycle?

[duncan webster 1Participant @duncanwebster1]

I've done 10 like that (wheels that is not locos) the others I machined a recess in the back face first and used that to grip using 4 jaw gripping inside the recess. No disc required, but you have to set up each wheel twice.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Luker on 02/04/2021 16:50:28:

[…]

… I personally think the problem lies on the tool side. Sorry I should have elaborated a little more in the initial post. I have had the same result with spoke’d and solid wheels, with different materials so this should have shifted the modal point, but the intervals between the chatter ‘marks’ were identical. This makes me think the problem is on the tool side.

.

.

If the chatter pattern is identical on both spoked and solid wheels, and on different materials, then of course I’m happy to believe that the tool [or its mount] is to blame.

MichaelG.

[WearyParticipant @weary]

Hello Luker,

LBSC's mandrel for turning locomotive wheels was fitted as follows:

"Chuck an odd casting or disc of metal a little smaller than the back of the wheel ….. recessing at the middle for about 1/32 in depth and 1 in. or so diameter" (quote from 'Virginia' notes, but similar wording appears for other builds) and then fitted with a mandrel which was subsequently turned to appropriate diameter. Thus the mandrel was principally for centering the wheel which was fully supported by the 'odd casting' or 'disc of metal' held in the chuck. The nut on the end of the mandrel was used to pull the wheel back into firm contact with the ad-hoc faceplate.

Regards,

Phil

[Nigel McBurney 1Participant @nigelmcburney1]

Its the method thats the problem, for a start the holding method is wrong,any large diameter disc held on a relatively small mandrel will be very prone to chatter,there is also a tendency when using carbide tooling to use the high speeds in the charts,high speeds lead to chatter unless the work is well supported. the machining method described ie plunge cutting i assume is achieving the metal removal in one cut if so may cut ok but when the tool stops feeding along the tool starts to produce a a chattered finish,the old adage should be respected do not let your tool rub keep it cutting or clear it from the work . The slight dwell when changing tool feed direction will cause tool chattering. The writer also states his method is faster,its a hobby why is there a need for speed,select the best method not the fastest. Looking at the lathe tool,I may be wrong but it looks like its essentially a form tool with angled face to produce the tapered flange and I assume it fed along the bed via the saddle so why is the top slide set over ? I have machined a fair number of brake discs /drums ,stationary engine flywheels and they have to be held formly to avoid chattered finish, For example when machining brake drums if the drum is held by the centre hole ,a poor chattered finish will result . set up a large thick cast iron disk with four /or more tapped holes in a four jaw ,face the disc off to get the face true bolt the drum true onto the fixture and use a brazed carbide toolbit with minimum tip rad ,in a big boring bar,slow speed and fine feed and a good finish is the result,care has to be taken not to rush the job,in the vintage world there may be no spares for a 1950s lorry and customer satisfaction is essential.I have only done a couple of sets of loco flanged wheels and got very good results using four chucks and a thee jaw with soft jaws ,no skinny mandrels ,good finish ,happy customer.

[LukerParticipant @luker]

Posted by Michael Gilligan on 02/04/2021 18:58:10:

If the chatter pattern is identical on both spoked and solid wheels, and on different materials, then of course I’m happy to believe that the tool [or its mount] is to blame.

MichaelG.

Top picture is of a spoked, tired wheel 150mm dia. Bottom picture is of a solid 65mm wheel. I think the pattern is very similar considering the large difference in parameters, but I'm not an expert in these things!

[LukerParticipant @luker]

Posted by Weary on 02/04/2021 19:36:45:

Hello Luker,

LBSC's mandrel for turning locomotive wheels was fitted as follows:

"Chuck an odd casting or disc of metal a little smaller than the back of the wheel ….. recessing at the middle for about 1/32 in depth and 1 in. or so diameter" (quote from 'Virginia' notes, but similar wording appears for other builds) and then fitted with a mandrel which was subsequently turned to appropriate diameter. Thus the mandrel was principally for centering the wheel which was fully supported by the 'odd casting' or 'disc of metal' held in the chuck. The nut on the end of the mandrel was used to pull the wheel back into firm contact with the ad-hoc faceplate.

Regards,

Phil

Hi Phil, I stand corrected. I just checked my Martin Evans book and he followed a similar approach. Looks like I found a novel way of doing things, and as a plus my wheel flanges have additional grip for those corners

[BufferParticipant @buffer]

When I had chatter I slowed the lathe right down and in the end pulled it over by hand for the last few revs and the chatter marks were all scraped away.

[LukerParticipant @luker]

Hi Nigel, all makes sense, but if you’ve machined over 50 wheels it’s more of a chore than fun. The beautiful thing about this hobby is you can never be bored, currently my interest is in developing an alternative alloy for steam cylinders as tin is becoming exorbitantly expensive; cast the first cylinders a few weeks ago. The little ‘skinny’ mandrel handles a 1.5mm roughing cut without complaining which is not bad considering I mix my cast iron to be harder on the outer profile for my non-tired wheels; this is of course with chromite sand in this area. The wheels I cast in this fashion actually outperform the tired ones.

I started restoring bikes when I was at school, I don’t recall having any problems clocking the drums and skimming. I do however recall battling with rebuilding and truing up the wheels. If you interested in vintages I’ve uploaded pics of my 58 and 25. I had to make the brake shoes for the 25 as they were missing.

This morning I did a few experiments on a spare wheel, and I found a few ways to get rid of the chatter. Buffer’s method worked also, thanks for that. I think this little exercise will make a nice write-up, thanks to everyone that pitched in and steered me in the right direction.

PS: Buffer can I mention your method? If so can you PM me your name for reference.

[Author]

Posts