I have a 9x 19 lathe and when I chucked up a 2 inch diam part in my 4 jaw, I get it trued up close to the jaws but then 3 inches out and it is out of whack.
So then I threw on my 3 jaw and my 3/4 inch harden ejector pin, I run into the same thing, get it zeroed in by the jaws but then 3 inches out its like .010 wobble
Any ideas?
wobble in lathe
Re: wobble in lathe
I hate to say this, but I wouldn't expect from a 9 x 19 unless it's of good quality.
Re: wobble in lathe
Need ideas not opinions
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mechanicalmagic
- Posts: 1431
- Joined: Sun Nov 04, 2007 12:11 am
- Location: Pleasanton, CA Land of perfect weather
Re: wobble in lathe
Learning to dial in a part at two places using a four jaw takes practice. The task is particularly difficult if the chuck is bell-mouthed.
If you had full contact on the jaws of the 3 jaw, then a soft hammer might allow you to get it closer than .010". Again, worn or bell-mouthed chucks are a problem.
If the lathe has a precision taper in the headstock: a good DTI can be used to see if it is running eccentric.
Dave J.
If you had full contact on the jaws of the 3 jaw, then a soft hammer might allow you to get it closer than .010". Again, worn or bell-mouthed chucks are a problem.
If the lathe has a precision taper in the headstock: a good DTI can be used to see if it is running eccentric.
Dave J.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.
Re: wobble in lathe
Google "grinding lathe chuck jaws" there are some videos about, good for the basic idea.
This is one of the very odd things many machinist have a mental block over.
There are better ways to load the jaws that seem to be shown on the videos.
Who knows, maybe you might want to rebuild scroll chucks, another mental block the average machinist suffers.
Anyway, the problems you discribe, do not have to be tolerated.
This is one of the very odd things many machinist have a mental block over.
There are better ways to load the jaws that seem to be shown on the videos.
Who knows, maybe you might want to rebuild scroll chucks, another mental block the average machinist suffers.
Anyway, the problems you discribe, do not have to be tolerated.
Re: wobble in lathe
First thing to check is that the chucks are seating properly. Does this use the A style chuck mount - a plate that the chuck is bolted to? Check for any dings / debris on the face of the mounting plate. Check the mounting plate runs true on the face. If not, remove it from the spindle to see if there's a problem with how it's mounted. If the faceplate runs true and the chuck is seating properly and still runs out, you probably need to grind the jaws.
Wayne
Wayne
Re: wobble in lathe
There is more to rebuilding a chuck than you might think. If all you need is a new bearing for the scroll to run it, then it a rather inexpensive fix. On the other hand if the slots the jaws move in are severely worn, then that is an entirely different story. If the slots are worn then most likely the scroll is worn to, then you have the gears to replace as well. I am not against repairing a chuck, since I am in the process of making a couple of new parts for my chuck. The thing is it more cost effective to replace than to rebuild. Usually the answer is yes as replacing is often less expensive than a rebuild. As far as I know no one offers over size jaws to fit in re-machined slots. So you would have the expense of machining and heat treating then grinding jaws to fit an over sized slot. I have seen some really sloppy chucks that were sent to the welding department for their welding positioners.roundnose wrote:Google "grinding lathe chuck jaws" there are some videos about, good for the basic idea.
This is one of the very odd things many machinist have a mental block over.
There are better ways to load the jaws that seem to be shown on the videos.
Who knows, maybe you might want to rebuild scroll chucks, another mental block the average machinist suffers.
Anyway, the problems you describe, do not have to be tolerated.
Then if you are just talking about grinding the jaws, then yes I have seen a few people who are afraid to do it. Those people often buy new jaws in the hope that fixes the problem.
Richard W.
Re: wobble in lathe
It does take practice, but is done quicker if you use short soft pads between the chuck jaws and the part. This allows for easy tapping in of the far end.mechanicalmagic wrote:Learning to dial in a part at two places using a four jaw takes practice. The task is particularly difficult if the chuck is bell-mouthed.
My experience if it you can move a part in a 3 jaw, then the chuck is worn bell mouth or its just plain wore out. If the chuck in question is new or near new, then you can bang or tap on the part all day and not get it dialed in. In which case you should take Harold's advise and bore soft jaws!mechanicalmagic wrote:If you had full contact on the jaws of the 3 jaw, then a soft hammer might allow you to get it closer than .010". Again, worn or bell-mouthed chucks are a problem.
I think the 9 X 20 has no taper, but a straight fit much like a flat back chuck. I tend to agree with Dave on this that checking the spindle for run out is the first thing to do. Then check for dings on the spindle face and back of the chucks.mechanicalmagic wrote:If the lathe has a precision taper in the headstock: a good DTI can be used to see if it is running eccentric.
Dave J.
Richard W.
Re: wobble in lathe
In 4 decades, and rebuilding dozens of scroll chucks, just never seen worn out jaw slots, or worn out scrolls. Even on chucks used on grinders.
Some chucks do have looser slots then others however.
I read that all the time from people that have never rebuilt chucks.
Two bad things happen from wear, the scroll center pivot wears, and the pinions force the scroll into the chucks front half inner face, causing wear there. Both repairable.
What will kill a scroll chuck is, if the front half is bent in from a crash. 6jaw chucks are much weaker on the front half, because so much is cut away for the jaw slots.
Anyway, for the "new person", when chucking a piece, clean the jaws, start clamping the piece while rotating the part against the force of cutting "normal cutting, this would be the top rotated toward the back of the machine" rotate and clamp at the same time.
This will help take up the slop in the the jaw slots, and scroll. Also, helps reduce the work from shifting from the force of cutting.
On factory chucks supplied with the Monarch EE lathe, one of the pinions is marked "M" this is the master pinion that was used for final "tuning in"-"grinding the jaws" at the Monarch factory, not the chuck makers.
Any 3 pinion chuck, one pinion will work better for run-out, and is easy to find, using the clamping method above.
Once the best pinion is found and marked, use the other two pinions only to loosen the chuck. This will spred the wear that occurs on the scrolls center pivot, and the action of the pinion gear pressing the scroll against the inside face of the front half of the chuck body.
Use only the master pinion to tighten the chuck.
Some chucks do have looser slots then others however.
I read that all the time from people that have never rebuilt chucks.
Two bad things happen from wear, the scroll center pivot wears, and the pinions force the scroll into the chucks front half inner face, causing wear there. Both repairable.
What will kill a scroll chuck is, if the front half is bent in from a crash. 6jaw chucks are much weaker on the front half, because so much is cut away for the jaw slots.
Anyway, for the "new person", when chucking a piece, clean the jaws, start clamping the piece while rotating the part against the force of cutting "normal cutting, this would be the top rotated toward the back of the machine" rotate and clamp at the same time.
This will help take up the slop in the the jaw slots, and scroll. Also, helps reduce the work from shifting from the force of cutting.
On factory chucks supplied with the Monarch EE lathe, one of the pinions is marked "M" this is the master pinion that was used for final "tuning in"-"grinding the jaws" at the Monarch factory, not the chuck makers.
Any 3 pinion chuck, one pinion will work better for run-out, and is easy to find, using the clamping method above.
Once the best pinion is found and marked, use the other two pinions only to loosen the chuck. This will spred the wear that occurs on the scrolls center pivot, and the action of the pinion gear pressing the scroll against the inside face of the front half of the chuck body.
Use only the master pinion to tighten the chuck.
Re: wobble in lathe
Repairing a worn scroll bearing can be as simple as thin shim stock...... Can work wonders.
Re: wobble in lathe
I have seen some that have had more than 1/32 of shake in the jaws.roundnose wrote:In 4 decades, and rebuilding dozens of scroll chucks, just never seen worn out jaw slots, or worn out scrolls. Even on chucks used on grinders.
Some chucks do have looser slots then others however.
Richard W.
Re: wobble in lathe
I suppose slots can become too worn, I just have not come across it. Though, some chucks are looser in the jaw slots then others, rotating the work when clamping seems to make that not a problem.
This chuck, a Buck 6"-6jaw is one of the most worn I have came across. A Hanford surplus, removed from a shot K&T dividing head. It must have clamped hundreds of thousands of parts.
The single pinion wore the front and rear chuck body hole radically egg shape- I sleeved the pinion OD around the key area- rebored the chuck halves. and installed a bushing in the back chuck half, for the small end of the pinion.
The wear was terrible on the scroll pivot to the point of actually breaking through the center bolt circle.
On this one, I used bronze for the pivot, I usually use steel pipe, I just had a piece of bronze handy.
The black handle Oring pick is pointing to the thrust pad on the front half, this was recut at the time of installing/cutting/bushing the worn pivot.
The back half was cleaned up also, where the gear side of the scroll dug itself in.
After the pivot, and the thrust areas on the chuck halves were cut, this caused excess end play for the scroll.
The chuck was bolted together with just the scroll, with a couple of pieces of thin lead wire on the scroll side at the front half thrust pads, taken back apart, the squished wire measure, the excess play removed by machining the rim on the rear chuck half, pointed out with the thread fish in the photo.
After those operations is when I remachined the chuck for the pinion problem.
Really, scroll chucks are not all that precision made in the first place, as the jaws are ground in the chuck at the factory. This is why jaws from a same make/style chuck will not run true when installed in another.
I shoot for about .0015 clearance scroll pivot- around .002 scroll end play, makes the chucks abit tight at first.
Then, set up for jaw grind.
Hopefully this pic will work,
That seemed to work,
I did take me a cold winter day to fix this free to me chuck, but, one must cost alot these days. I feel its worth it.
On the machine with no wobble, a test bar will run within a couple of tenths 8" out. Repeats within a couple of tenths at a given size, better then .002" within its full range. "nice"
This chuck, a Buck 6"-6jaw is one of the most worn I have came across. A Hanford surplus, removed from a shot K&T dividing head. It must have clamped hundreds of thousands of parts.
The single pinion wore the front and rear chuck body hole radically egg shape- I sleeved the pinion OD around the key area- rebored the chuck halves. and installed a bushing in the back chuck half, for the small end of the pinion.
The wear was terrible on the scroll pivot to the point of actually breaking through the center bolt circle.
On this one, I used bronze for the pivot, I usually use steel pipe, I just had a piece of bronze handy.
The black handle Oring pick is pointing to the thrust pad on the front half, this was recut at the time of installing/cutting/bushing the worn pivot.
The back half was cleaned up also, where the gear side of the scroll dug itself in.
After the pivot, and the thrust areas on the chuck halves were cut, this caused excess end play for the scroll.
The chuck was bolted together with just the scroll, with a couple of pieces of thin lead wire on the scroll side at the front half thrust pads, taken back apart, the squished wire measure, the excess play removed by machining the rim on the rear chuck half, pointed out with the thread fish in the photo.
After those operations is when I remachined the chuck for the pinion problem.
Really, scroll chucks are not all that precision made in the first place, as the jaws are ground in the chuck at the factory. This is why jaws from a same make/style chuck will not run true when installed in another.
I shoot for about .0015 clearance scroll pivot- around .002 scroll end play, makes the chucks abit tight at first.
Then, set up for jaw grind.
Hopefully this pic will work,
That seemed to work,
I did take me a cold winter day to fix this free to me chuck, but, one must cost alot these days. I feel its worth it.
On the machine with no wobble, a test bar will run within a couple of tenths 8" out. Repeats within a couple of tenths at a given size, better then .002" within its full range. "nice"
