What's new
What's new

General knowledge please

dceg

Plastic
Joined
Nov 11, 2019
Hello, my name is Dan in Des Moines IA. I am here for some assistance on making my Sheppard lathe work better. I am not a machinist or engineer so my language may be incorrect as it applies. I have recently made adj on Gibbs leveling and tail stock alignment. The bronze spindle bearings have .0005” movement horizontal and .001” vertical. The old cushman chuck has run out of .005” probably more if I measure correctly. The saddle does not have Gibbs but has plates near apron and opposite side to keep carriage from lifting. I’ve snug them so maybe .003” lift is found if I pry up. I’m carful to sharpen cutting tool and set center height but at times have trouble getting a .010” cut close to chuck for checking and correcting taper 5” away from chuck. I suspect the chuck is not holding the work good enough. Tried remounting cold roll stock and tighten many times. Chatter of course. Should I be buying a new chuck? Crossfeed and coumpond slides (Gibbs) have been checked but that to has little movement.
 

Attachments

  • 1E94BE0C-636E-4763-927B-06D742E13E24.jpg
    1E94BE0C-636E-4763-927B-06D742E13E24.jpg
    19.1 KB · Views: 194
  • image.jpg
    image.jpg
    93 KB · Views: 242
Might be helpful if needed

http://vintagemachinery.org/pubs/1617/5795.pdf

Old worn out three jaw chucks are way more trouble that they are worth. If you get a chuck, ONLY go for a four jaw that YOU control run out on.

Yes it takes a little learning, but so does the rest of the machining idea

Now if a new or better chuck comes along, you need to get used to the idea that it is not going to fit the Sheppard unless you make it fit - like using the old back plate that DOES fit the lathe
 
I had same problem with a larger 4 jaw measures 9”. Those jaws rattle when slowly turning spindle empty. I just made a quill to fit tailstock but taper was a problem so several measurements made and corrections but 8” long I now have only .0015 taper. Time consuming. Yes thank you I have the mid 60’s edition. Have read cover to cover at least three times. Many things learned from Tubalcain. Again I’m no pro but have lived around machine tools all my life. This ol girl I cut my teeth on. Nothing beats weight to overcomes chatter.
 

Attachments

  • 4650BDFD-7049-43C9-88CC-FD6A15B742A3.jpg
    4650BDFD-7049-43C9-88CC-FD6A15B742A3.jpg
    18.2 KB · Views: 165
I'm not sure I'm understanding your description of the problem

'trouble getting a .010” cut close to chuck for checking and correcting taper 5” away from chuck.'

But that doesn't sound like anything having to do with the plates under the apron or uplift of the saddle. And 0.0005 of spindle runout does not seem overly excessive for that large/old a lathe.

If you're suspecting chuck problems causing the chatter, perhaps mounting a stiff (1") bar in the chuck and measuring how much rock or deflection when you push/pull about 12" out on the bar beyond the chuck.

Possible your chuck is just bell-mouthed and regrinding (plenty of old threads about how to do that correctly) will correct some of that chatter.
 
Also not sure what you mean by

'same thing with the 4-jaw whose jaws rattle when you turn the spindle empty.'

If your 4-jaw isn't clamped down on a piece of stock, the jaws are gonna rattle. There's gonna be some backlash in the threads of each jaw that tightening down on a piece of stock will eliminate.
 
I have read and viewed countless info on making lathes run true. some info is left out. Yes a 1" stock 6" or so out from chuck with no tail stock to support to check lathe twist. First thing is a cold roll stock of 1" will wobble and I confirmed accuracy first with mic. A flat surface plate does not indicate it is bent, I blame chuck on that problem. My 4 jaw is really bad. Compared to an older but I believe a good 4 Jaw used on the tail stock on old monster above. Those jaws are snug. no slop. I'm curently having the back plate made so I can try it. I mentioned the plates on the saddle because I would imagine if there is any room for movement I will have chatter. I'm only describing the lathe and what I've done. perhaps none of this is relaevent. Oooh spell check. I did check pulling up on shaft mounted in chuck and wow yes it spins the dial. I was'st sure if .001" on spindle was an issue. Just asking for things to check. Yes the chuck key is not in the correct position. However Dad passed away and a family member was assisting. No worries No electricity for someone to get hurt. Good observation.
 
Re: The spindle bearing play. The horizontal play at 0.0005" sounds OK. The vertical play, at 0.001" may be a little excessive, but I suspect that is not your worst problem and you can live with it for now. On that issue, most journal bearing head stocks are made in two pieces which are bolted together with shims between them. Since the cutting forces on the work piece are generally vertical and in the upward direction, you will usually get more bearing wear in the vertical direction and the upper part of the spindle bearing will wear the most. If your bearing is a two piece with shims, removing about 0.0005" from that shim stack would be an almost perfect repair for that condition.

The saddle is pressed in the downward direction by the cutting forces so it will usually stay on top of the ways. A Vee way will then stabilize it in the horizontal (front-back) direction so movement there is not usually an issue. And it, the saddle, will not normally move upward. Any keepers that are there that would prevent any horizontal or upward motion are of only secondary importance and a rather large amount of clearance is usually OK. The only time that I know of when this is not true is when some kind of milling attachment is mounted on the saddle or cross slide and a milling cutter is mounted in the spindle. The milling forces, when milling in the lathe, can be in any direction and must be carefully considered.

It is hard to tell weather your chucks are OK or in need of maintenance and/or replacement.

Three jaw chucks often have 0.005" of runout or even more. A scroll is not the most precise way of positioning the jaws and wear on that scroll and on the jaws can produce a variety of runout problems. And those runout numbers can vary when chucking different diameter stock because different positions on the scroll are being used. I have an old 3 jaw chuck where the runout exceeds 0.010" in some conditions. I tried grinding the jaws, but there was little or no improvement. I concluded that the scroll and jaws were worn in an irregular manner. I purchased a new chuck. But if your runout is 0.005" or less, a new chuck may not be an improvement.

The four jaw, independent chuck should allow you to "dial in" the centering to any level of accuracy that you wish. But, if the jaws are worn, then a bell mouth condition may exist where they are worn more near the outer edge. This will mean that you can not rely on stock being gripped in the same manner two times in a row. It can tilt one way and then another. Even cutting forces may move it in bell mouth jaws. If it is a brand name chuck, you may be able to purchase new jaws from the manufacturer. If it is a less known or import chuck your only resort may be to replace the whole chuck.

Oh, some jaws are made in two pieces: the lower half which engages the scroll or tightening screws and an upper half that grips the work. In this type of chuck jaw you can buy replacements for the upper half.

Posting some photos with closer views of the spindle bearings and the chucks may help us to make suggestions.
 
Thanks for that clear message. The bearings are not two halves. I have considered cutting the bearing the thickness of a hacksaw blade at the 3 o'clock position.using shims to take up the material removed minus .0005" Maybe I should just cut the bearing in half and adj from there. I would get less distortion on bearing if one full half was lowered evenly, YES ? I am quite certain I have bell mouth on jaws as noticed with long stock chucked in and severe movement when force applied. Cushman lathe chuck parts still available ? No the jaws are single piece otherwise it would be easier to tool post grind the jaws. Waiting on backplate to be made and trued on my lathe before mounting the other 9" chuck. I have read a lot about using a 6" vs larger capable size chucks but I would think a larger chuck acting as a flywheel to rotate through the cutting force of tool would be beneficial. On other hand I'm concerned that heavy rotating mass would be detrimental to the already slightly loose bearings. I've been searching for trustworthy lesser prices imports but that has me concerned.
 
Don’t go cutting any bearings yet. It doesn’t sound like you’ve ruled out the more basic bellmouthed Chuck jaws yet. Don’t risk destroying the lathe until you’ve sorted out where the chatter is coming from.

If you chuck up a 1” bar and wiggle it back and forth, how much play do you get at 12” out from the chuck?
 
I’m not to make this lathe NASA’s newest so to make that clear. I tested deflection on travel using 1” cold roll shaft. @12” out 15 lbs pull .012” @12” out 25 lbs pull .025” @6” out 15 lbs pull .004” @6” out 25 lbs pull .007” I found info on lathe tolerances by a German engineer showing how to check and where and at what tolerances allowed. I’ve lost that site. I know this is not going to run like new again but it would be a good starting point I’d think.
 
Yeah. Wow. That's a lot of deflection. Way too much.

I'm guessing enough to tell if the bar is rocking in the jaws (bellmouth) or the spindle being loose.

0.250 of deflection with 25 lbs of pull and you should be able to look at the jaws and see if there's contact across the entire jaw.
 
Ya I knew I'd screw up as stated in my first post. I edited my last post to to state .025" not 1/4"
 
You might blue up the part with blue or just a sharpy and look close at markings the jaws put on the part to see it marked for a distance along the part..
The part may run way out of true with run out and wobble but taking a cut with a very sharp bit with the bit having perhaps 5* side and back rake with perhaps the part only at 4" sticking out from the chuck..The turned part area should be straight and true for the length of that cut. look at your bit as it sets in the tool holder to see there it has 8 to 12* clearance under the side cutting edge and that there is clearance under the very point..and is fingernail shaving sharp

*Most often one has the compound at a 20 or 30 degree angle to the right, the tool post about middle and travel with moving the saddle toward the head stock. Set at 29 1/2 it is ready for turning a thread.

Travel with the compound slide is used for turning a taper but is not so/as good for a straight part.

QT Johnoder: go for a four jaw that YOU control run out on.When you get used to a 4 jaw it will only take 2 minuets to center a part.
 








 
Back
Top