Calling All Machinists - How to Hold (and turn) a Wheel In Lathe

[1reason]

Well, here I am again, Tuesday (which is now today - I started this post yesterday and am now back) is the big race day, and I'm still attempting to get my mini lathe from HF setup to make great wheels that are so light, they float in the air and so round, the car wins before the pin drops....

The first time I hit the "calling all machinists" alarm, I was met with wonderful and actionable advice that brought my machining skills to new heights. Now I'm hoping to figure out wheels.

I feel bad because my seven year old has watched his older brothers win and he's been out in the shop working on the car a lot more than they did at his age, so he's motivated, but I didn't get much done due to a head-cold during the time I thought we would build (and then this).... Anyway, here's where I'm at now...

The setup HF 7 x 12 mini lathe that I added a four jaw chuck to. I have a couple of indicators to measure both inside and outside diameters, and have learned to dial it in to about a thousand, or as tight as I think I can get it within the lathes own actual tolerance (which is a whole different discussion)

I have a collet holder and collets.

First problem, is centering the wheel. If I use a Mandrel tool, the wheel isn't centered and "wobbles" (I think the correct term is it has runout, and I "think" it's from the screw stem that screws into the Mandrel, and not the mandrel itself (I have four different mandrels, and the issue is the same with each.

The wobble/runout could be from how the wheel sets on the mandrel, but I'm not sure how to fix that neither.

I saw a picture of a wheel mounted similar to the above, but instead of using a collet, the chuck held a round wheel holder often used with manual wheel shavers and hub sanders. The wheeel was then held in place using a metal tube when was then held in place using a live center. Pictures can be seen here -> http://pddr.proboards.com/thread/4058/lathe-mandrel-prep-wheels

using the same system seems to be my best option (especially given the amount of time left), albeit this isn't the last race, and every other time I've asked, I've received "just what was needed".

So what say you, machinists?

Thanks!

Bob

 

[TRE]

there are several ways to do this i use a pin..some cut there own pin

 

[pony express]

I am not a machinist and gave up trying to cut wheels as good as John, but if you persist then have a machine shop make a wheel mandrel that fits the wheels you want to cut. The other problems I had was the lathe chuck was cheap and I could see wobble if I placed just a straight pin in the chuck. I could see wobble as the pin was spinning. That is bad news when you start cutting. To get around a bad chuck you can replace the lathe chuck altogether with your collett. You'll need a arbor with a taper that matches your machine. What you have right now is a straight shank collett holder. Get a collett holder with the machine taper and it will get rid of more wobble.

 

[mike-E]

i honestly have no idea how the pro wheels are cut. if i were you i would cut a pin about 7/8 to an inch long and about .003-.005 bigger than the wheel bore. without removing it from the lathe, i would then polish the pin to a mirror spending extra time on the end at the lower grits so it comes out slightly tapered. i would use only the friction fit on the bores to hold the wheels and take tiny cuts using a very sharp tool at high speed. high speed will most likely give you trouble with a 4 jaw. if you have a three jaw you would be better off using that without the collett holder. to do any inside cutting on the wheel i would use a different set-up. i would start out with 1-1/2''o.d. 1'' i.d. tubing and bore a shallow hole (3/8'') that the previously o.d. cut wheels slightly press into. you need tubing stock because you will be able to insert a rod through the backside of your lathe to tap the wheels back out.

 

[1reason]

I am not a machinist and gave up trying to cut wheels as good as John, but if you persist then have a machine shop make a wheel mandrel that fits the wheels you want to cut. The other problems I had was the lathe chuck was cheap and I could see wobble if I placed just a straight pin in the chuck. I could see wobble as the pin was spinning. That is bad news when you start cutting. To get around a bad chuck you can replace the lathe chuck altogether with your collett. You'll need a arbor with a taper that matches your machine. What you have right now is a straight shank collett holder. Get a collett holder with the machine taper and it will get rid of more wobble.

I don't think my son and I are about to cut wheels as good as John based on other products I've bought and was happy with, albeit, I've come this far......(plus it's fun, frustrating, but fun).

I think I understand what you mean by the straight shank collet holder vs. a machine taper, but not sure. Do you mind posting a link(s) and/or pictures so I can see the difference. I'll Google it too, but I already have several collet holders and maybe I have what you're talking about??? Along the same lines, I think you mean the very top part that screws in to tighten, but maybe you mean the entire collet holder???

Thanks!

 

[1reason]

i honestly have no idea how the pro wheels are cut. if i were you i would cut a pin about 7/8 to an inch long and about .003-.005 bigger than the wheel bore. without removing it from the lathe, i would then polish the pin to a mirror spending extra time on the end at the lower grits so it comes out slightly tapered. i would use only the friction fit on the bores to hold the wheels and take tiny cuts using a very sharp tool at high speed. high speed will most likely give you trouble with a 4 jaw. if you have a three jaw you would be better off using that without the collett holder. to do any inside cutting on the wheel i would use a different set-up. i would start out with 1-1/2''o.d. 1'' i.d. tubing and bore a shallow hole (3/8'') that the previously o.d. cut wheels slightly press into. you need tubing stock because you will be able to insert a rod through the backside of your lathe to tap the wheels back out.

Thanks for your reply, I appreciate it.

Why is a four jaw chuck not as good at high speed? I have the three jaw that came with the lathe, so it's not hard for me to switch to a three jaw, but my thought was the four jaw is more accurate?

Thanks

Bob

 

[Vitamin K]

I am still in the "I wish I had a lathe" category, though I've managed to glean some info over the years.

Those Derbyworx mandrels are fine for polishing wheel treads, but worthless for maching wheels, as they have too much inherent radial runout.

To really get a true wheel, you need a perfectly centered pin on which to mount it. What a lot of folks do is to turn down a new pin at the beginning of the wheel turning process, and mount the wheel on the newly produced mandrel. This is just a friction-interference fit, so you'll want your mandrel at just the right size to where the wheel fits on snugly.

This means, of course, that the size of the bore of the wheel will determine the thickness of mandrel that you turn!

I think I saw somewhere a recommendation that you sort wheels by bore size (you'd need a set of gage pins to measure), and work the larger ones first, adjusting your mandrel to fit each smaller size.

 

[mike-E]

a 4 jaw will allow a more accurate mounting of an uncut piece but it also has a lot more rotating mass that most small lathes cant handle at high speeds without excessive vibration. a collet system that is made for your lathe would be the most accurate though you should still cut a new pin every time. if you want to be able to cut pins and switch them out while maintaining accuracy you will need to spend about ten grand on a precision machine. there is a thread on here where the o.p. was asking similar questions and they were told that they should take some night classes on machining. this is true. learning to cut precision parts from internet advice is like learning a new language while being taught to drive at the same time. your best bet is to just jump on the lathe and cut parts.

 

[pony express]

I missed the computer era and don't know how to post pictures and such. The part of the collett system that in your picture that rests inside of the lathe chuck's jaws is the shank and what is in the photo is a straight shank (no taper). You can get a collett shank with a MT taper (in place of the straight shank) like on a drill press so you bypass the chuck jaws altogether. You remove the lathe chuck altogether and simply push the collect holder(arbor) with the MT taper into the hole where the lathe chuck was covering. I think the MT stands for Morse Taper. The arbor has a Morse Taper and usual drill press chuck has the corresponding Jacobs taper. You can get a collett system with a Morse taper so you can bypass using a chuck to hold the collett. The less parts the less chance for poor work results.

 

[pony express]

when I first got my lathe I read how great the 4 jaw chucks were and got one. Cheap 4 jaw chucks are as worthless as the cheap 3 jaw ones. remember the 4 jaws have to come together exactly at the same time which is tough to manufacture. I got tired of cheap components and gave up on the lathe.

 

[mike-E]

i consider this guy to be the best youtuber when it comes to explaining machining techniques and set-ups. especially when it comes to turning. this video is very relevant to what you are trying to accomplish. if, and when, you fully grasp the concept he is teaching here a light will go on guaranteed.

 

[1reason]

i consider this guy to be the best youtuber when it comes to explaining machining techniques and set-ups. especially when it comes to turning. this video is very relevant to what you are trying to accomplish. if, and when, you fully grasp the concept he is teaching here a light will go on guaranteed./QUOTE]

Thanks and I agree, his stuff is really good (at least it appears to be for me).

I posted this in another thread, but in the hopes this may get looked at first, I now have a new problem. The Wheel's diameter is increasing on about half the tread, the half that runs closest to the car. I have no idea why, and it's counter-intuitive for me because it's the smaller diameter part that appears to be getting cut first.

 

[mike-E]

o.k. look up how to sharpen a lathe tool on youtube. there are dozens of vids on the subject. i recommend "mr. pete". when it comes to the part about putting a slight radius at the tip ignore it. you will not need that for plastic. spin your lathe as fast as possible and if you are hand feeding the cut do not dwell in one spot. keep the tool moving across the tread. your tool is dull right now and the section of the wheel closest to the car is flexing away from the cut because the wall is thin and has no support like the area closest to the outer hub. you just need to sharpen your tool is all.

 

[1reason]

o.k. look up how to sharpen a lathe tool on youtube. there are dozens of vids on the subject. i recommend "mr. pete". when it comes to the part about putting a slight radius at the tip ignore it. you will not need that for plastic. spin your lathe as fast as possible and if you are hand feeding the cut do not dwell in one spot. keep the tool moving across the tread. your tool is dull right now and the section of the wheel closest to the car is flexing away from the cut because the wall is thin and has no support like the area closest to the outer hub. you just need to sharpen your tool is all.

Thanks, and I'm glad I asked. I was thinking maybe I needed to slow down the wheel. Gonna do what you said about using a sharper tool, and spin it faster. Will report back, and thank you.

 

[mike-E]

one more thing i assumed you knew and might not. the tip of your tool has to be at the very center of rotation or ever so slightly below. (by just a few thousands). if you are above center the tool will not actually be cutting, but instead be rubbing material off. this will also cause extra pressure on the wheel tread and cause it to deflect away at the less stiff inner half. hope this makes sense.

 

[1reason]

Thanks again Mike.

Not only did I not know that, I thought slightly higher was better than lower. I have learned to use a thick feeler guage to determine height. I was using a six inch machinist ruler, but somehow it's missing. With three sons, having things "missing" is something I'm afraid I've become used to....

Looking for a video on this now.

Thanks

Bob

 

[mike-E]

Ha, i have a few "borrowers" running around my house too. though i usually get "lucky" and find my tools and other belongings with the lawnmower!! let me know how those wheels turn out.

 

[1reason]

Ha, i have a few "borrowers" running around my house too. though i usually get "lucky" and find my tools and other belongings with the lawnmower!! let me know how those wheels turn out.

HA, oh yes.... I have found the lawnmower method of finding things to be a highly effective strategy, albeit when found, it's not a good thing.....

Wow, can't thank you enough. I will admit, I was worried when I turned the dial up to full speed. The wheels I worked on last night look like they came from the factory on the inside cuts, including the inside vertical. I haven't tried the outside tread yet, where I had an issue with bowing out, but based on the adjustments made so far, I feel like I'm on the right track (cheesy pun, I know).

Three wheels worked on last night. all three started at 2.7 grams and ~ .0685 in tread thickness. Finished tread is ~ .04 or less. On the vertical part, I thinned one to the point I can see slight light coming through when using a bright light source, and the other two I can't. I'm thinking of using the thin walled wheel as the front wheel.

I'm even able to give the very outside a little "lip" with the thought that it will help keep the part touching the track from bending and operating more like a "flat tire". Theory anyway....

Big race is tomorrow. Still not sure we're going to be ready or not

 

[1reason]

i consider this guy to be the best youtuber when it comes to explaining machining techniques and set-ups. especially when it comes to turning. this video is very relevant to what you are trying to accomplish. if, and when, you fully grasp the concept he is teaching here a light will go on guaranteed.

Thanks, yeah he's great