Turning Wheels on a Mini Lathe.

[Stan Pope]

No description.

Oh!

Unfortunately, no chucking it into the lathe for me. It's 3 feet long.

My spindle is hollow and allows a 5/8" dia rad to extend through the spindle and out the chuck! Handy! That feature was something that I didn't know to look for when I was purchasing ... I was lucky that it came that way! For all bad that I can say about Cntrl Mach, they did copy from some good designs! I suppose that the technology is old enough that patent protection long since expired ... which, I suppose, is an issue, at least if it is to be imported.

For cutting the mandrel ... consider cutting the face down to an oversized center pin, say 1/8" dia. 6 or 7 0.010" face cuts should leave enough pin.
Then measure the pin diameter and cut away 1/2 to 2/3 of the excess, cutting parallel to the spindle axis. Measure/cut/measure /cut ... until you have about 0.101" dia pin. Then work the pin into a taper to about 0.097" at the outer end using a fine file held against the spinning pin. When you get close, measure with a wheel bore! When the wheel almost seats fully, switch to emery paper to smooth out the pin and take the last 0.0005 to 0.0010" off the pin. At the same time use emery paper on the mandrel face to smooth that off. Ideally, when you finish, the wheel slides onto the mandrel with the spoke face flush against mandrel face with only the gentlest of pressure, and, once on, will not slide sideways at all. At that point, you will not damage the bore and teh wheels should be as low runout as the rest of your lathe is capable of.

I don't think that there is a problem with 2 or 3" of mandrel stock protruding from the chuck, unless the chuck lacks strength to hold it. That gives you room for a couple dozen "mandrel re-do's".

If you have a dial indicator, put it on the pin and see just how well you did. When you are done running wheels, try a couple times to remove the mandrel, chuck it up again, and measure the runout then. Repeat a few times to see how well you lathe performs.

[mechanic]

Stan Pope I made a mandrel set like yours and it is much faster and nicer than what I was using. Thanks for sharing the great idea

[ScoJo]

Thank you thank you thank you for this thread. We just finished our mandrel and turned our first wheel with it. Hard to quantify our runout because our dial gauge is only marked every 0.001", but in contrast to last year where the needle would move through 0.001 to 0.002", this year with the first wheel we can barely see it move at all.

[Stan Pope]

Way to go, guys!!!

Another measure of result is to rotate the finished wheel 180 degrees on the mandrel, then reclamp. Now use your dial indicator to make runout measurements again. So long as the wheel is not free to slide on the face of the mandrel, the part runout will be 1/2 of whatever you measure. If the mandrel was well done, the number should be really small!

The ultimate truth is to take the wheel to an independent TIR measurement device ... a snug fit pin resting in side-by-side v-grooves, pressed into the grooves by the force of the dial indicator pin.

[tjeffrey]

Stan, why the spoke surface versus the outer edge of the wheel for orientation? is it the letters? If so, if you had pinecar wheels with no letter would you orient to the spokes or the outer most surface of the wheel?

[Stan Pope]

Stan, why the spoke surface versus the outer edge of the wheel for orientation? is it the letters? If so, if you had pinecar wheels with no letter would you orient to the spokes or the outer most surface of the wheel?

I haven't looked at wheels other than BSA, so I can't tell you what I'd do with others. But I can tell you what I'd think about when deciding.

First, inquire which features of the wheel are truest to the untouched bore. Useful features require some ability to slide the plane of the tool around so as to center on the bore.

Second, inquire which features of the wheel can function as clamping surfaces. Important considerations include substantially flat areas on opposite sides of the wheel. If the clamping surfaces are not almost exactly opposite, the clamp will not be able to hold the wheel with sufficient strength. The clamp must hold the wheel with sufficient strength to prevent sideways movement and/or strain between the bore end and the locating pin.

Recall that step 1 in the wheel prep is to use my bore ream guide to true the bore to the face. Then step 2 is to use the bore and face to clamp the wheel onto the lathe mandrel. Turning a fresh mandrel for each run requires (or, at least, makes desirable) a simple mandrel geometry. And, of course, both ream guide and mandrel must use the same features for locating!

[tjeffrey]

Thanks Stan. The outside spoke area of the Pinecar wheels are slopped. They are the Mag type wheels with real spokes. The inside area is flat and could position the tailstock support against them, but I'm not machinist enough to cut a mandrel to fit the outside spoke area. I could reverse the wheel on the mandral and use the inside spoke flat area for orientation of the reamer and the mandrel, but then I have the same problem holding the opposite slopped side of the spokes with the tailstock support.

There is a small ring on the outer diameter of the spoke area on the outside, but it is only 1/16" or so wide. I don't think it's enough surface to rely upon. Based on your observations I will use the outer sidewall of the wheel. It doesn't have letters, is very sturdy and has a 1/8" area on the inside opposite it where I can make a tailstock holding device.

[Stan Pope]

...
I will use the outer sidewall of the wheel. It doesn't have letters, is very sturdy and has a 1/8" area on the inside opposite it where I can make a tailstock holding device.

It sounds like you have found a workable plan! Only the mandrel need be easily machined. The clamp (from the tailstock) can be reused as is.

[chromegsx]

You ever try lathe with awana wheels? the material is so soft that it would seem difficult to turn accurately. I wanted to do more to the wheels to lighten them and tweak them but didn't realize how soft the material was and ruined the first set. Got another set and just polished them up the best I could tonight.

[Stan Pope]

You ever try lathe with awana wheels? the material is so soft that it would seem difficult to turn accurately. I wanted to do more to the wheels to lighten them and tweak them but didn't realize how soft the material was and ruined the first set. Got another set and just polished them up the best I could tonight.

Haven't tried 'em. If faced with the need, I might try packing 'em in dry ice for a while before starting to cut 'em! Dunno if that would be cold enough to stiffen 'em up or not, though.

Probably not a good activity for youngsters ... maybe not for oldsters either!

IIRC, good ventilation is needed, and January in Illinois is not a good time for ventilation!

[FinePine]

Hi Stan. If your chuck doesn't give you the chucking repeatability you need, consider eliminating the chuck! The mini-lathe spindle has a #3 Morse taper in it, no? If so, you may consider making a wheel mandrel out of a Morse taper blank that fits directly into the spindle bore, eliminating the need for a chuck or collet completely. Mark the orientation of the mandrel to the spindle and always match that orientation when reinserting. I think you can get a #3 to #1 adapter, so the blanks will be cheaper, or you can try making your own.

I've done something similar on my Unimat 3 lathe, and repeatability is very good.

Something like:
http://www.sherline.com/3055inst.htm" target="_blank
or
http://www.victornet.com/cgi-bin/victor ... arbors:275" target="_blank

-Stephen

[FatSebastian]

I've done something similar on my Unimat 3 lathe, and repeatability is very good

Intriguing! Thanks for the tip.

How much effort is involved in removing the spindle, etc.?

Could you quantify (put a number on) just how good "very good" repeatability is?

[Stan Pope]

Neat idea! Thanks!

[FinePine]

How much effort is involved in removing the spindle, etc.?

Could you quantify (put a number on) just how good "very good" repeatability is?

The Unimat 3 does not have a Morse taper, just a slip fit with a centralizing chamfer. Repeatibility was good enough that I couldn't measure it with a regular dial indicator. I do not have a dial test indicator, which should be used for such fine measurements, but I would guess it runs less than .0002" or .0003".

A Morse taper should do better than that, I would expect, if all the mating surfaces are kept clean, and the orientation is observed. The orientation wouldn't be an issue on a very good lathe, but with the Chinese stuff, who knows. Good practice anyway.

The Morse tapers use a wedging angle that will bind enough to stay put and transmit the required torque, but not get permanently stuck. You just tap them out from the back side using a bar that just fits in the ID of the spindle. To put one in you either tap it in lightly (with wood or something to protect the face) or you can pull it in from the back side with all-thread and nuts. Easier than changing a drill bit. Please note that I have never used a Harbor Freight mini-lathe, so I might be missing something here, but I don't think so. You ought to be able to go tap out your 3-jaw chuck in the same way to see what it is like.

Here's someone who made his own blanks, but I think they are cheap enough that buying is the better option.

http://www.projectsinmetal.com/shop-tip ... -easy-way/" target="_blank

[FinePine]

Neat idea! Thanks!

The lesson on the importance and difficulty of maintaining concentricity may suffer, however, since your students won't have to go through the effort of preparing the mandrel for their own use.