Turning down wheels on a lathe

[narrowminded]

Thanks for all the ideas folks—  I've been away from TRW for a few days.

The lathe in question is this one from a few years back:

https://littlemachineshop.com/products/product_view.php?ProductID=4959

Yes, and my goal is to actually operate these things.

-Dave

That's the same lathe I have under the Harbor Freight brand and only 10" bed.  The 10" bed is adequate for my work and imperative for my space.  If I had the room I would have the 14" bed.  And Little Giant is a good supplier and good for advice.  Example: their quick change tool post is THE way to go for reasons not often clear until you've used a few.  It's this one: https://littlemachineshop.com/products/product_view.php?ProductID=3112

A low cost but decent tool supplier to machine shops is Shars.com   They handle relatively low cost tools but as a real machine shop supplier they are a pretty reliable quality buffer.  The quality is generally decent at a good price.  They may even have the toolpost mentioned above and certainly will have the tool holders although you might be ahead to get Little Machine Shop's #3112 set if you're not perfectly comfortable with what you're ordering.  You could check for best price.

Do you have a decent .0005" test indicator?  Here's a low cost but decent Shars set that can get you started. Lookup #303-3203B for $29.50 and add #303-3213 dovetail swivel clamp for $11.15.  Useful in mill and lathe setup checking part runout, tailstock center, and the like.  In your mill or drill press for finding hole centers, squaring drill press table or mill head, etc.

A grinder with fine stone and wheel dresser for tool sharpening?  That could be a Harbor Freight order.  They also carry an assortment of HSS tool blanks for a good price.  https://www.harborfreight.com/5-piece-m2-high-speed-steel-mini-tool-bits-for-metalworking-lathes-40641.html  Get two while you're at it.

That's some quick stuff off the top of my head.  Checking some Youtube videos might be helpful for operation guidance, especially setting cutting tools on center.  This is CRITICAL!

[railnerd]

That's some quick stuff off the top of my head.  Checking some Youtube videos might be helpful for operation guidance, especially setting cutting tools on center.  This is CRITICAL!

Thanks so much for the tips.  I've been spending so much more time on YouTube watching machining videos than TV. 

-Dave

[mmagliaro]

I, for one, would like to see just exactly how people grip an N Scale wheel in a lathe (or mill) so you can really hold it straight and steady, and cut on it, without it popping out of the fixture or crushing.

I have tried holding them in a chuck or collet (like a 6-jaw mill collet for nice even pressure and grip).  It sorta kinda works, but isn't reliable.  There is very little surface on the tread to clutch in the jaws, and even less when you allow for a spacer to keep the flange away from the face of the jaws so you can get the cutting tool on the flange.

I am about to experiment with a hollow collet chuck (the type with a straight shank that is bored all the way through).  I am thinking that once the wheel is held in the collet, a long threaded rod could go right through the wheel center, with a nut/washer against the wheel, and another nut/washer at the back of the chuck shaft, to prevent the wheel from trying to creep out of the jaws while cutting.

Any photos of how you actually hold these wheels in a lathe (or mill) ?

[narrowminded]

I, for one, would like to see just exactly how people grip an N Scale wheel in a lathe (or mill) so you can really hold it straight and steady, and cut on it, without it popping out of the fixture or crushing.

I have tried holding them in a chuck or collet (like a 6-jaw mill collet for nice even pressure and grip).  It sorta kinda works, but isn't reliable.  There is very little surface on the tread to clutch in the jaws, and even less when you allow for a spacer to keep the flange away from the face of the jaws so you can get the cutting tool on the flange.

I am about to experiment with a hollow collet chuck (the type with a straight shank that is bored all the way through).  I am thinking that once the wheel is held in the collet, a long threaded rod could go right through the wheel center, with a nut/washer against the wheel, and another nut/washer at the back of the chuck shaft, to prevent the wheel from trying to creep out of the jaws while cutting.

Any photos of how you actually hold these wheels in a lathe (or mill) ?

I would probably consider gripping them in a 5c emergency collet (or R-8), precisely machined with the wheel flange diameter and depth, shouldered to just grip the flange diameter, the axle, or the tread, depending on what you're trying to do.  Because these are machined in place on the machine that they are to run in, they run true as can be with little to no effort.  There are extended nose units available too if you are trying to get out away from the chuck for some reason.  Running up close, as in machining a traction tire groove, the cutting tool will probably have to be ground for the service so it can be working very close to the collet face. 

A shallow pocket to grip the flange for cutting a traction tire or something on the outboard side of the wheel.  Inboard could be done too but would take some careful measurement of the wheel's angle (measured in the lathe) and then careful setup of the compound to be sure the taper you are machining is correct.  This is where you would use a .0005" (or better) indicator and use three points for measuring.  Indicate it to be sure it's running true and then two points in Z and one in X (or Y, think sine plate), then calculate the angle from those measurements.

Measure the part this way and then confirm your angle setting the same way, against an indicated true, straight bar gripped in the head.  Once you know the angle you're after you might scale your measuring points up for setting the lathe compound angle to make life easier getting it set.  And if you're feeling frisky, forget all of that angle measuring and use just a straight bore that single line grips the tread somewhere in the middle of its width, still shouldered square in the bottom of the bore.  You don't need a crushing grip for such small cuts, especially with sharp cutters and light cuts, so might well get away with that.  I'd try it.

And once you understand this approach and if runout isn't extremely critical (.001"/ .002"?) you might be able to come up with variations of your own based on your available tooling.  You might machine a bushing with an OD to go into a standard collet (or more crudely, your chuck ) and the ID prepped as needed.  Machine the bushing very accurately on the ID and OD so that little collapsing action is needed.  When the bushing is complete, slit on one side only.  This should run decently true especially if the dimensions of the bushing are good.  If you are using your chuck, mark the collet you're making to a specific jaw so you can repeat the position.  If using your chuck you should indicate the part each time you install it just to be sure it settled in to the proper position.  Fiddly but gets you through.

And it might be wise to machine the bushing from brass as it machines nicely so can be machined accurately and with a good finish.  I've also used aluminum, depending on the grip area, but brass is less prone to crushing at the face. 

You may be making your own boring bar for a bore this small.  And with a small bar don't have a big radius on the tool nose.  Sharp to .002" maximum.  Also, a very sharp cutting edge so it induces the lowest possible spring in the bar as well as a nice finish.  I would strongly consider HSS (old drill shank or broken end mill in a pinch?) ground to shape and hand stoned for a very sharp edge. This gives you the ability to make very light cuts accurately, especially in brass. 

In case you haven't seen one, here are some links to some simple emergency collets.  BTW, this is one of the easiest ways to repeatedly chuck up turned parts when you have to flip them end to end to finish the opposite side while being sure you hold good concentricity to an already machined diameter from the first step. Collet machined in place in the machine they will be running in, concentricity assured, and bored to any size needed, not trying to make a standard collet fit the bill.

https://www.shars.com/5c-emergency-collet-1-4-1
https://www.shars.com/r8-emergency-collet
https://shophardinge.com/assets/PDFfiles/B008C.pdf

And with cruder, bigger parts there's always a chuck with available soft jaws.   Machine the jaws to your need. https://www.shars.com/products/workholding/lathe-chuck-jaws

BTW, this is basically the way I set up my 24" wheels that are made with just a flat face to machine custom faces and drilled patterns.  I grip the flange.  A block machined in much the same way described for gripping in the mill vise and a collet in the lathe.  Any done in production will be machined in one setup in a CNC lathe with live tooling.  That is slick but doesn't lend itself to setting up for anything less than a LOT of pieces.

[mmagliaro]

Thanks, Mark.

I have heard of emergency collets.  I hadn't considered using them to actually make a custom holder for every wheelsize, however.

My thought with the ER collets in a collet chuck was that they are pretty forgiving and have a relatively wide clamping range so you only need about 5-6 collets to cover every size of N Scale wheel there is.    My experience with gripping wheels at all is that collets work better on these little wheels because they apply even, "rounded" pressure around the most of the perimiter of the wheel (or flange), as opposed to a chuck, which bites down in only 3 or 4 places where the jaws are.  The likelihood of making indentations or deforming the wheel is higher... even though I have done this in a chuck before!

There are also step collets (the kind that look like a "crater" with steps down the inside walls so you can grip things of varying diameters).  Those look like they would work really well for gripping the flange to allow cutting traction tire grooves, if you just got hold of an assortment that covered the wheel sizes we typically use.  Of course, the cutter would have to be shaped to kind of curve down in there, but it ought to work.  Like you said, the cutting pressures we need for these wheels are pretty light.  N Scale wheels are not very hard in the scheme of things.

Well, thank you for all your thoughtful education, as always.  For now, since the ER collets are coming in the mail, I will set some wheels up in them and see how that does.

-- Max

[narrowminded]

I'm not aware of any emergency collets made for the ER design for the following reasons.

The ER's are very popular and have many applications but started as tool holding collets with full shank length inserted to full collet bore depth.  This is important for how the collet grips, collapsing from both ends.  That is part of the theory of them, outstanding grip and repeatable true running... when inserted full depth.  Also, as they are used under their max rated size they start to reduce their grip area, becoming line grip based on the number of splits.  That is generally not a problem as long as there is a full length in the collet bore.  BUT, this is important, less than full length inserted into the collet bore allows the back side of the collet to collapse unsupported and distorts the bore grip but also can shatter the back end as it collapses excessively.  I hope that description is clear. 

One patch for that is to put a plug of the same diameter that will be gripped in the front, into the back/ depth of the collet bore to allow the collet to spring equally front and rear, as intended.  The size match should be pretty accurate (.001" maybe .002"?).  One more thing, depending on the ER collet holder nut, I'm not sure that it won't get in the way when trying to get right up at that face.

I'm also not sure how the very shallow grip of an existing wheel will be able to be reliably squared to an ER collet bore.  That's part of the reason for emergency collets being readily available in R-8 and 5c with a few additional types from Jacobs, maybe some others, but always a style with the slits and collapsing on one end.  You can shoulder them for a square stop.

What you might be able to do to use the ER's is to machine a full length sleeve that fits a larger diameter collet than the bore you'll need, allowing maybe 1/16" to 1/8" wall (?), and then drill the one end about 1/2 to 3/4 of the way through to relieve the center, then adding the necessary features and bottom shoulder at the face end, then saw split the bushing from the face end up to the drilled relief depth.  This should all be very close tolerance to minimize the flex of any portion of the latch up.  You might also be able to extend the front of the bushing a very small amount to get some front clearance from the nut.  Not too far but maybe just enough to help.

On first try, I found this video that has some of the idea using a 5c for a similar purpose.  It also has a .0005" indicator shown, although being used for carriage travel, not sweeping center, then a regular indicator being used for accurate reading of the cross slide, and finally gauge pins for measuring a small bore.  All sorts of machining goodness.   Hope this helps.

Edit add: BTW, another very handy tool is the gauge pins shown at the end of that video, used for measuring his bore.  I have two sets for my regular train work.  One is .011" through .060" and the second set is .061" through .250".  All of those pins are in .001" increments affording very accurate small hole measurement, but can also be passed between features for gap measurement, setting a jaw depth in a mill setup, whatever strikes you.  Use your imagination.

[mmagliaro]

Mark, I hear you on how the ER collets collapse.  But I got them and tried them, and I must say, it is easier to do than you might think - probably because the forces we need on an N Scale wheel aren't that high.  Also, the range on an ER32 collet is about .039"

I got an ER32 chuck and several collets to cover all the N Scale wheel sizes I could think of.  It is a straight shank, not a tapered shank made for my spindle (which it MT3).  I did that on purpose, because the straight shank chucks have a hole bored through them to the back, which will allow for "improvements", like a long holding bolt through the wheel.

But for a quick and dirty experiment, I just chucked a Trix K4 wheel in the collet, use a piece of .012" brass shim to get the wheel to hang below the collet face uniformly (I push the wheel into the collet, only tighten it "snug", and then use the shim to space the wheel away from the collet face by .012" evenly all around, and then tighten for keeps).

I cut the flange down and then just use a jewelers file to dress off each side.  I am not going for an RP25 profile here - just a clean, smooth, slightly-rounded edge that will work and look good.

So... it all worked just fine.  No slipping, no crushing the wheel, etc.

The truly amazing thing to me was how good this collet chuck is on run-out.  These were relatively cheap China-made collets and collet chuck from CME Tools.  But the collet chuck, INSERTED INTO MY REGULAR 3-jaw CHUCK, in the mill, has only about .0005" runout.  I tested it with a dial indicator running against the outside of the collet chuck.  Then I put a drill bit into the chuck so I could run the indicator on something actually chucked in it.  Runout was about .0015".  I still find this amazing considering it is a collet chuck, held in a 3-jaw chuck, in a low-end hobby mill.

Anyhoo.... at least from my end, I see this as a solution.  I don't really need to cut any wheels right now.  But hopefully, I can motivate myself to cut another one and take some photos to show how it fits in the chuck and how the cutting works.

[narrowminded]

Excellent!  And you gripped on the tapered tread, correct?  Collets do tend to be reliably true.  And if the chuck is too, you're in!     I'm glad it worked out for you.

[mmagliaro]

Excellent!  And you gripped on the tapered tread, correct?  Collets do tend to be reliably true.  And if the chuck is too, you're in!     I'm glad it worked out for you.

Yep.  I just put the tread into the collet, tighten it, and it holds plenty firm enough to cut the flange.

[narrowminded]

Yep.  I just put the tread into the collet, tighten it, and it holds plenty firm enough to cut the flange.

That actually doesn't surprise me.  As I said in a previous post, "I'd try it".

It's always tough trying to give advice on these matters without knowing the recipient's experience, feel, and such.   That shouldn't be such a concern with someone like yourself, evidenced by the parts you've produced with your mill.   I hope my posts aren't received in anything but the spirit in which they are offered and that the information is either helpful or possibly confirming what you were already thinking.   

And I would love to see the things you'd produce with a lathe in your bag of tricks.   You'd make such good use of one and would have NO trouble picking up on its operation.