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View Full Version : Could use some expertise on a lathe cam lock spindle backplate fit up



hammerfest
06-24-2009, 01:31 AM
Gents--I could use a bit of advice on some troubles I am having with a D1-4 Cam Lock Backplate that I am trying to fit up to an Hardinge-Sjogren 2J Speed Collet Chuck.

My problem is that I can not get the face of the backplate that mates up against the headstock spindle to run parallel to the face of the backplate that mates to the chuck. The headstock spindle has zero runout both on the face and the male taper, so it's not a spindle problem and all other chucks I have fit right.

I can set the backplate up on the spindle and machine it to essentially zero runout. Remove it. Remount the plate in the same position using the same holes for the cam lock pins and the face has any where between .002 to .006 runout on the face that the chuck mounts to. The run out on the top of the backplate continually is less than .001. I have tried tightening the cam lock pins, trying different holes, remachining the face and every time I end up with the same result. When the chuck is mounted and I am measuring runout six inches or so from the backplate it is now over .012, which is totally unacceptable.

I have racked my brain to to figure out the problem and have guessed that the female taper on the backplate is allowing the plate to center properly on the spindle but it must not be allowing the plate to lock up tight against the mating flat on the spindle. I believe the only way to fix this would be to slightly enlarge the female taper hole to allow the plate to slide on further. My concern is if I go too much I have lost the centering ability. And then the whole job turns goes western and it's a rodeo.....

There are no burrs or other issues that would would prevent the two surfaces from seating flat.

I know you guys are smarter than me and I would value any experience you might have getting these type of cam lock spindles to marry up chucks and such.

In advance thanks.

Jim Shaper
06-24-2009, 01:46 AM
D spindle noses are supposed to locate the chuck on the taper. If you're not seated on that taper, then you won't ever get repeatability.

The only way to make the two fit if they don't is to machine down the back face of the adapter until the taper seats. I've heard different figures for the gap that should remain between the spindle face and the adapter face, but it's typically repeated as .001" of daylight.

I've had to fix the fit of 2 of my chucks that didn't come with the machine by doing this. Take it slow and you should be fine.

luthor
06-24-2009, 01:55 AM
There should be no gap at all, it should locate on the taper and pull up tight on the face.

b2u44
06-24-2009, 02:11 AM
Is there any gap between the flat faces on the spindle and backplate? If there is, that could lead to your problems and the only corrective action that I can see would be to enlarge the hole in the backplate.

What make/model lathe are you trying to mount this backplate to? If it's a good quality machine, then I'd say correct the backplates. I had an experience with a low-quality lathe where the spindle wasn't ground right. The original chuck that came with the machine fit fine, but any good-quality chucks (Bison) would have the same problem you describe. Turned out that the diameter of the spindle taper was too big. After reducing the taper diameter a bit, the chucks fit great with very good repeatability between mountings.

Ian B
06-24-2009, 04:17 AM
Hammerfest,

I think you're spot on in your diagnosis. Getting a camlock to fit properly looks like a very difficult job to me - one I haven't even tried. Suggestion to fix it:

Put the backplate on the spindle, try it a few times and get it to run with the greatest possible runout - worst case, whereby you should have contact on one side of the flat face. Then measure the axial runout on a pitch circle equal to the diameter of the camlock taper (2.5").

Divide the total indicated runout by 2.

Mount the backplate to machine the taper, set the tool to just touch the taper's surface, then advance the lathe's carriage by the runout divided by 2, Take a skim, you should be there.

Good luck,

Ian

Glenn Wegman
06-24-2009, 05:51 AM
Taper dimensions

http://shopswarf.orconhosting.net.nz/chuckmt.html

oldtiffie
06-24-2009, 07:23 AM
Have you checked the female taper on the back-plate for correctness as regards:
- that it is truly round;
- that the angle (7.125 deg Atan = 0.125 = 1/8) is correct;
- that the female dimension "B" on the back-plate is at least the upper limit of male dimension"B" (2.5005 + 0.0005" = 2.501") on the nose of the lathe spindle?

A good preliminary taper check is to use the lathe male taper as "master" and try the "problem" taper and a couple of the "acceptable" tapers you have against the "master" taper using "Prussian Blue" as you would for a morse taper fit. At least it will be a start and a bit more information to base a decision on before proceeding to do any more machining.

The taper of 7.125 degrees is actually a 1 in 8 taper which means that not only will a 0.001" in movement on the cross-slide take off 0.002" on the diameter but the end of the taper will have moved 8 x 0.001" = 0.008" along the axis. That can be very helpful in taper-fitting.

If it were my job, I'd seriously consider re-machining the back-plate female taper and the back face that locates on the front face of the lathe spindle and then re-mounting it on the lathe spindle and re-machining the front face of the backing plate.

Have you got a copy of the specification sheet for the chuck? If so it will give you the relevant data that was accepted/acceptable at manufacture.

Here are two typical specification sheets for a 125mm (~5") and a 160mm (~ 6.3") chucks for my lathe which does not have a taper but has a parallel spigot.

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/3-jaw_chuck_specs1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/3-jaw_chuck_specs2.jpg

Jim Shaper
06-24-2009, 12:56 PM
There should be no gap at all, it should locate on the taper and pull up tight on the face.

If it's tight on the face, how can you be sure it's located on the taper? Even with prussian blue, you're going to have smut on the taper throwing off your alignment.

If there's a small gap, you know you're pulling against the taper and not simply seated against the face. The face doesn't hold any of the axial load anyway - it's all on the nose taper. If you've got a properly fit chuck, it should require breaking the "seat" with a deadblow to remove the chuck just like your mill spindle with an R8.

The cam locks just pull it tight and hold it there. The taper is taking the load.

Ian B
06-24-2009, 01:49 PM
Jim,

I think he knows it's not seating on the face because he measures runout on the face, not the periphery. If the taper was loose and the face was tight, this would be the other way around.

My lathe has a D1-8 nose. When tightened, there's no sign of a gap on the face. I know that the taper is locating, because when I've had a chuck on there and I loosen all 6 cams, the chuck stays put until I give it a hefty whack with a rubber mallet.

Ian

Peter.
06-24-2009, 01:50 PM
Mine pulls up on the face. I think that taper is too narrow for very accurate repeatability, not like the long-nose taper.

lakeside53
06-24-2009, 04:35 PM
I see two different opinions above - a gap is required... a gap is not... so.. what is it (according to the official specification)?

rklopp
06-24-2009, 05:08 PM
No gap. Think about it. How could you possibly rely on the wimpy short taper plus luck to control wobble runout? You'd need all the luck in the world to get the cams to exactly the right tightness in the right sequence so that the gap was uniform. That's nuts. No gap. No gap. No gap.

ASME B5.9 says the gap to the master ring gauge for D1-3 is to be +0.001/-0.000, which is anticipated to produce a slight interference fit on the taper. For D1-4, the gauge gap is +0.002/-0.000. I don't see a number for the expected gap (before pull-up) for in-tolerance chucks mentioned explicitly in the standard. However, the master ring gauge is to be a "Prussian blue fit" to the master plug (i.e., spindle) gauge, and the master plug gauge is to be at the small end of the spindle nose tolerance. Thus, the gauges should represent the smallest in-tolerance spindle and smallest chuck tapers. The chucks are supposed to have a +0.002/-0.000 gap to the master spindle gage. Apparently, the gap before pull-up for real-world chucks and spindles will be in the range of +0.004 to -0.000 for in-tolerance D1-4 parts. You get +0.004 if both the chuck and spindle have 0.002 gaps to the gauges and 0.000 if both have 0.000 gaps. You'd preferably want a gap because it is difficult to distinguish no gap from actual slop with the taper part of the fit.

tattoomike68
06-24-2009, 05:14 PM
There should not be a gap, the backing plate was not done right or the cams need drawn in farther to suck it up tight.

The taper on a cam lock is very short so all it does is center the chuck and the flat gets it strait.

If you a a nit picking old fart that will take the time to machine the backing plate right then you will have no problem geting it right.

For all we know tha backing blate was machined by a 8 year old chinese girl and it was her first month of full time work. :eek:

nheng
06-24-2009, 06:41 PM
A gap is required prior to tightening the cams. I don't have the number handy but it isn't much. It is measured with the mating plate hand held against the taper.

I'm pretty sure I've posted the numbers here but can't find anything anymore. Guess it wasn't on this site but here is the info:

added - from a good German chuck data sheet, the gap should be no more than 0.02mm which is 0.00078" with the chuck is "pressed on lightly", or in other words, by hand.

Den

tattoomike68
06-24-2009, 07:21 PM
A gap is required prior to tightening the cams. I don't have the number handy but it isn't much. It is measured with the mating plate hand held against the taper.

I'm pretty sure I've posted the numbers here but can't find anything anymore. Guess it wasn't on this site but here is the info:

added - from a good German chuck data sheet, the gap should be no more than 0.02mm which is 0.00078" with the chuck is "pressed on lightly", or in other words, by hand.

Den

When the cams are engaged there should be no gap, no way will a .0005" fealer gauge insert into the gap. Iv run europian machines and well as china, tiawan and not a one of them had some gap allowence.

damn , sometimes I think im dealing with smart folks then other times its numbnard dickweeds. the cam locks are not working, HELLO!

smiller6912
06-24-2009, 08:55 PM
I was having a problem with a gap and getting the chuck square. When I talked to the manufacturer they told me to whack the face of the chuck with a rubber hammer while tightening the cams to help draw it up tight. Bingo, I can draw it up flat and square with ease every time now.

nheng
06-24-2009, 09:55 PM
When the cams are engaged there should be no gap, no way will a .0005" fealer gauge insert into the gap. Iv run europian machines and well as china, tiawan and not a one of them had some gap allowence.

damn , sometimes I think im dealing with smart folks then other times its numbnard dickweeds. the cam locks are not working, HELLO!

Tattoomike68, What they're saying is that when lightly pressed on by hand, you want a gap and that gap will close when the cams are engaged. The gap guarantees that when you tighten up, the taper is controlling the centering, as it should be.

Another reference, from Rohm workholding, indicates that the gap should be in the 0.02mm to 0.05mm range when "lightly fastened".

See the top of page 16 here: http://www.roehm.biz/fileadmin/Downloads/Produkte/Bedienungsanleitung/RN_398_neutral.pdf

oldtiffie
06-24-2009, 10:47 PM
Thanks nheng.

That has to be the definitive work on the subject - many thanks.

Pages 10>17 should be compulsory reading for just about any of us here - but particularly so in discussions on this topic as well as "problem solving" in the shop.

A great post and a great link/reference.

hammerfest
06-24-2009, 11:13 PM
Gentlemen--thank you all for your valuable time to respond and offer experience and recommendations. I believe I may have found the potential source of the problem.

That eight-year old Chinese girl working in the dirt floor basement of her parents home, next to the underground coal mine where her ten-year old brother works, and the steel mill down the street where her older sister works, next to the metal scrap recycler where her six-year younger sister sorts though the junk to find materials to make the pins for the cam locks, it turns out that the purchased middle-eastern Indian five-year old who cuts and threads the pins was actually the source of the problem.

The pins were not engaging enough to properly suck up the backplate to the face of the spindle. As a result there was a gap and this thing went western on me. After backing out the pins several rotations, re-installing, refacing, removal, reinstalling, and re-indicating, I appeared to have perhaps solved the problem.

Unfortunately this family has done me in because I cut the OD to an exact fit for the chuck earlier in this clam bake. So I "chuck" this up to experience and call it a fifty dollar lesson.

I am reaching for a few catalogs to find a high quality backplate of the Bison, Rohm, Huron, or Sjogren variety. Unless I get this operation to a zero runout on the chuck I have defeated the whole purpose of using it. The price of the Chuck New is approximately $1500, so I'll now pop the extra dollars to do it right.

This time I will install it, face it, turn a few thou off the OD, pull it out, re-intstall in the same holes, indicate and repeat the process no less than six times every time it better be zero runout all around, then I get to sizing it to the finished size.

Again, thank you for the help.