PDA

View Full Version : Chuck balance question and max rpm



medwards
07-10-2009, 05:20 PM
I'm contemplating buying a new 3 jaw chuck for my 13" Clausing Colchester. I'm currently using the 8" 3 jaw L0 mount Burnerd chuck that probably came new with the lathe in 1966. I've though about getting a fresh set of jaws for the chuck, but that's half way to the cost of a new set-tru bison chuck. The chuck will noticeably vibrate this ~1600 lb. lathe at anything more than 700 rpm. I don't have a 5C collet setup for this lathe, so I can't even use half the rpm range of the lathe. I don't see any reasons other than casting density issues that would caust this. The chuck body doesn't have excessive run out. Depending on much I chuck into the jaws of the chuck, I can get as low as .002" run out on a piece of 5/8" drill rod.

My questions: Are there any rules with RPM and chuck size? Is a newer 8" bison set tru chuck going to be better balanced than an old Burnerd chuck? Am I asking too much of scrolling chuck, should I be using 5C above 700 rpm?

Thanks in advance for any input.
Mike Edwards

Walter
07-10-2009, 05:49 PM
Med, while there's no real reason why one cannot run a chuck at or above those speeds, I'd dig a bit deeper trying to find out why you have the "balance" issues.

While I don't know what you have for a lathe, here's what I've run into personally. I run a Clausing 5419 (http://www.lathes.co.uk/clausing/page3.html) and have an issue similar to what you describe, but I have found that the issue actually resides in the pulleys on the motor and intermediate shaft, not the chuck. They are worn and have a chunk missing and cause a vibration that I originally thought was in my chuck. I yanked the chuck all apart, re-trued the back plate, disassembled the chuck, cleaned and lubricated it, then reassembled with << .001 runout showing on the outer body of the chuck. Still there. The chuck being large and somewhat heavy seems to exacerbate the problem with the pulleys. I can pop my old 4 jaw on which is light and not have 1/2 the problem, but if I equal out the weights I get that issue to show up more prominently.The faster I run the lathe the worse the vibration is. Obviously the collett setup isn't an issue.

So, before you spend cash hoping to solve a problem, (even though a set tru would be a great addition) you may want to do a bit more back tracing. Then spend on the set tru and enjoy it ;)

medwards
07-10-2009, 06:04 PM
Walter,

Mine is an older 6500 series (pic below).

Mine has a gear box drive spindle, where yours is a variable speed drive. If the motor or belt drive pulleys were the issue it would be unbalanced at any speed because the motor and belt drive are always turning the same rpm. The largest gears in the headstock are 4" at most and none are missing teeth, so I doubt the ballance issue is there. I'm not going to dismiss the posibility of the balance problem being in the lathe, I just think it's ulikely. I'll pull the chuck off tonight and run the spindle empty at high rpm to confirm.

I do have a 10" 4 jaw and 12" face plate, but both are still mostly rough casting on the backsides.

Mike

http://i112.photobucket.com/albums/n177/edwardsmt/CIMG0216-1.jpg

Walter
07-10-2009, 06:57 PM
Mike,

Another thought. I'm not entirely sure how accurate a wheel balancer is, but maybe pull the chuck off and see if it can be spun on one of them. Should be pretty cheap to do and might get you some answers.

knedvecki
07-10-2009, 07:16 PM
You could possibly do a static balance on the chuck using a grinding wheel balance type of arbor and rollers.

philbur
07-10-2009, 07:22 PM
An 8" chuck should have a maximum allowable rpm of at least 2500 (it should be marked) so I would have thought that it would be adequately balanced for the rated rpm. Have you stripped the chuck to look for missing/damaged parts. You could remount the naked body to do a test run, to give some mass. Have you checked the spindle bearing preload.

Just some thoughts from a novice
Phil:)

medwards
07-10-2009, 07:56 PM
I pulled the chuck off and ran the spindle empty through all the gears up to max 1800 rpm. There was a hint of vibration at 1800 rpm, but nothing compared to what it would have had at 900 with the chuck on.

Walter and Knedvecki - I'll certainly check my options on checking the balance of the chuck. I would sure hate to spend $1K on a new chuck only to have the same vibration.

Philbur -I couldn't find any markings for max rpm on the chuck. Only info is that it is a Burnderd model# N51LOTJ Made in England. I have not checked the preload on the bearings, but I'm not sure it is adjustable on this lathe.

Here is a excerpt from the lathes.co.uk site.

"The forged, high-tensile steel 1.5-inch (38 mm) bore spindle ran in Gamet "One-micron Precision" bearings - Gamet being a separate company within the controlling 600 Group who also supplied many other machine-tool makers. A small pre-load was applied to the bearings by spring pressure - that immediately behind the spindle nose being a double-row type with a single-row at the rear. Gamet claimed that the "unique design ... ensures minimum temperature rise and accurate running of the spindle throughout the speed range" "

I went through the majority of the mechanicals on this lathe about two months ago and all was well. It got new belts, oil and a complete rebuild of the apron and cross slide. I also went through the chucks. Nothing stood out in the 3 jaw chuck other than some wear to the scroll and pinions.

aboard_epsilon
07-10-2009, 07:58 PM
may be full of swarf.

strip it clean it ..

then try again .

all the best.markj

philbur
07-10-2009, 08:09 PM
I would strip the chuck and check for damage/missing parts. If it is OK then spindle bearings on a 1966 machine would have to be near the top of my list. A DI on top of the chuck and a 4x2 under, with firm but gentle leverage would show up any obvious bearing issue.

Phil:)


I pulled the chuck off and ran the spindle empty through all the gears up to max 1800 rpm. There was a hint of vibration at 1800 rpm, but nothing compared to what it would have had at 900 with the chuck on.

Walter and Knedvecki - I'll certainly check my options on checking the balance of the chuck. I would sure hate to spend $1K on a new chuck only to have the same vibration.

Philbur -I couldn't find any markings for max rpm on the chuck. Only info is that it is a Burnderd model# N51LOTJ Made in England. I have not checked the preload on the bearings, but I'm not sure it is adjustable on this lathe.

Here is a excerpt from the lathes.co.uk site.

"The forged, high-tensile steel 1.5-inch (38 mm) bore spindle ran in Gamet "One-micron Precision" bearings - Gamet being a separate company within the controlling 600 Group who also supplied many other machine-tool makers. A small pre-load was applied to the bearings by spring pressure - that immediately behind the spindle nose being a double-row type with a single-row at the rear. Gamet claimed that the "unique design ... ensures minimum temperature rise and accurate running of the spindle throughout the speed range" "

I went through the majority of the mechanicals on this lathe about two months ago and all was well. It got new belts, oil and a complete rebuild of the apron and cross slide. I also went through the chucks. Nothing stood out in the 3 jaw chuck other than some wear to the scroll and pinions.

wierdscience
07-10-2009, 08:23 PM
Check for missing chuck body bolts,had that on a chuck once.I'm assuming the chuck runs true right?If it's running out excessivly,check the key in the long taper mount and see if it's deformed.That will keep the taper from seating tight.

The Bison chucks are excellent units,they're website has the specs for the chucks including max RPM.

http://www.toolmex.com/products/bison-workholding/

tattoomike68
07-10-2009, 08:25 PM
You could possibly do a static balance on the chuck using a grinding wheel balance type of arbor and rollers.


I agree you can test it to a small degree that way. it will get you close.

I dont think many of you folks have machines that will bust a chuck from shear RPM alone. the force will make the jaws loose to a degree but not if you get a firm bite on the part.( a fine balence at that point)

Now if you have a 30 HP Hardinge CNC that turns 4,000 RPM you best not bolt on a cheapo chuck thats not rated for such a tool.

I think you will be fine just stay with an 8" chuck or smaller. Iv run lots of 10 inch chucks at 2,500 and would say for the most part thats about as fast as you should ask from a chuck of that size.

If the machine hops around at 700 RPM then you have to mount the damn thing right, even my wimpy midas 1220 $1,000 smithy I have at home will turn the 8 inch 4 jaw I have at 1,500 RPM and it does it just fine.

balancing is a long slow deal but not bad. I made some mandels just for that to do 12 inch fan rotors to 4,000 rpm +. that was a static test, to do a dynamic 2 axis test is more involved but not hard to do in a good shop. maybe others can explain a dynamic 2 axis high speed balance better than I can.

Anyway I dont think you can get too much RMP from you lathe as long as the chuck is mounted right and not a cheapo casting thats crap to start with.

Are you turning parts under .125"? thats where you need rpm.

oldtiffie
07-11-2009, 12:14 AM
Originally Posted by knedvecki
You could possibly do a static balance on the chuck using a grinding wheel balance type of arbor and rollers.


I agree you can test it to a small degree that way. it will get you close.

I dont think many of you folks have machines that will bust a chuck from shear RPM alone. the force will make the jaws loose to a degree but not if you get a firm bite on the part.( a fine balence at that point)

Now if you have a 30 HP Hardinge CNC that turns 4,000 RPM you best not bolt on a cheapo chuck thats not rated for such a tool.

I think you will be fine just stay with an 8" chuck or smaller. Iv run lots of 10 inch chucks at 2,500 and would say for the most part thats about as fast as you should ask from a chuck of that size.

If the machine hops around at 700 RPM then you have to mount the damn thing right, even my wimpy midas 1220 $1,000 smithy I have at home will turn the 8 inch 4 jaw I have at 1,500 RPM and it does it just fine.

balancing is a long slow deal but not bad. I made some mandels just for that to do 12 inch fan rotors to 4,000 rpm +. that was a static test, to do a dynamic 2 axis test is more involved but not hard to do in a good shop. maybe others can explain a dynamic 2 axis high speed balance better than I can.
Anyway I dont think you can get too much RMP from you lathe as long as the chuck is mounted right and not a cheapo casting thats crap to start with.

Are you turning parts under .125"? thats where you need rpm.

The problem with static balancing - as for a grinding wheel on a mandrel/arbor which is sitting on horizontal knife-edges is that it is quite possible and quite liable to be statically balanced with weights of different mass and not in the same radial plane.

As soon as the statically-balanced "wheel" spins up centripetal forces take over such that different masses not only have different centripetal forces but cause substantial "twisting" moments.

For example - on a tyre/wheel dynamic balancer, set the weights for static balance and then spin the wheel up and all of a sudden it is a whole new ball game as regards forces and the mass and positioning of the rim-mounted balancing weights needed to get a satisfactory balance through a pre-set speed range.

Re-wound electric motors are quite often "re-balanced" (think: grinder spindles) for optimum performance.

I'd be very hesitant about using a statically (only) balanced wheel (or chuck) in a situation that required dynamic balancing.

Even a small "out of balance" can cause a surprisingly considerable other-wise "unexplainable" eccentricity in parts turned at high speeds.

Put a glass of water on your lathe head-stock and run the lathe through its speed range and note the "rippling effect" on the surface of the water. If the glass wants to "walk" off the head-stock, you have a problem.

Same trick works well on a grinder to test the spindle alone and then the "spindle with wheel attached" situation/s.

Machinery's Handbook has quite an extensive cover on the topic.

http://en.wikipedia.org/wiki/Balancing_machine

http://en.wikipedia.org/wiki/Tire_balance

medwards
07-11-2009, 11:49 AM
Markj - No swarf in the chuck. I pulled it a apart a while ago and cleaned and lubed it.

Philbur - Spindle bearings are a 4 letter work for any colchester owner. I've read about people paying as much as $1500 for a single gamet precision bearing for a colchester.

I pryed on the spindle with a 2x4 like you described. The 2x4 was about 3' long and I pryed up against the spindle, leveraging off the bed, with quite a bit of force. My indicator showed .0012" movement. I would stay offset until I rotated the spindle and then it would go back into place with .0006" runout. Because the spindle bearings are spring loaded, I'm sure I was just moving the bearings a bit against the spring pressure. Then when I spun the spindle, they would move back into place.

weirdscience - No missing bolts. Key is good and taper is clean of any swarf. I always clean the taper with the palm of my hand before mounting the chuck.

tatoomike68 - I agree that it would help to bolt the machine to the floor, but that's only going to mask the balance problem, not fix it. I need the rpm for both small diameter parts and for some plastic parts. I really wish I had all the parts to run 5c collets.

medwards
07-11-2009, 11:54 AM
Today, I'm going to disassemble the chuck and run just the backplate. If that goes well, I'll add the chuck body. Then add the guts of the chuck and see how it goes.

Thanks all for you help so far.

Mike

medwards
07-16-2009, 09:28 PM
And the winner is.


If the machine hops around at 700 RPM then you have to mount the damn thing right.

Your prize is 3 shims I used to level the lathe.

I put the chuck on in pieces and it slowly got worse with each piece. But, in the process of bolting the chuck on and off, I hit the lathe and it moved a bit. I had it sitting on three steel pads/ shims where the colchester manual says to put them. For some reason it was teetering a little. I pulled the pads/ shims and set it on the floor and no more vibration all the way up to 1800 rpm with the chuck on.

Great, vibration problem solved. So I found a set of Cushman chuck jaws on ebay that matched the dimensions of the Burnerd jaws. $11 later I bolted them onto the chuck and now I can clearly see that the t-slots and master jaws are worn enough that the new unworn jaws will only grip a piece of stock closest to the chuck. I guess I could discribe them as being camed out.

But, at least I feel confident that a new chuck will run vibration free on the lathe now.