[tjd10684]

back story:

i just got (well actually i got it in Feb) a Birmingham 1340GH. i am starting to get pretty familiar with it and starting to notice some of its quarks. such as when i take a peice of tool steel and chuck it up when i go to take my first skim pass i ALWAYS only hit "high" spots. when i was doing this with plastic it was easy enough to say well it must be the stock but with ground round stock as soon as i touch it should be contacting all the way around. so i decided to measure it. it turns out that when i put the stock in and tighten it down its actually spinning the stock off center by .00425 again this is not really a problem when i have a bunch of room on the stock but if i want to re- chuck something and just take a .001 cut i cant because its .00425 off center. this got me thinking maybe the chuck is off center so i indicated the outside of the chuck and its off .00025 thats within reason. so it has to be the jaws of the chuck. that got me thinking maybe i can make some soft jaws. and bore them out so my part always spins concentric. so what im thinking i need is hardened backs and aluminum jaws. the aluminum jaws are no problem but the hardened backs would be.

Real Question:
is something like this really universal so that i can get a set of these and make my own soft jaws
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[juergenwt]

tgd- don't panic! I assume everything is brand new? First make sure the chuck is "on" clean. 3-jaw chuck, you will have some run out. You are not looking at some real precision equipment here. If the chuck runs good, than I would say the jaws are not very good, but with a three jaw you can easy have .004 run out. Try re-clamping a few times with an indicator along side. Also a slight tap with a piece of lead or copper could help. How far out are you cutting? Let me tell you that even with a precision 6jaw you will have problems holding within .001 TIR. I think you are asking to much from what you have got.
As far as using "Master Jaws" and than boring out soft jaws to get more accuracy-forget it. Those are mostly used to .hold "special sizes". You will NOT repeat within .001. To do this right you will need a lot more experience. Save you money.

[tjd10684]

Their were punch marks near the posts on the chuck and on the head. I was going under the assumption that the marks indicated the best position. then i remembered an old saying never trust anyones measurements unless they agree with your own. so i took the chuck off cleaned it really well and shifted the punch mark and measured the run out again 0.0025 much better i think i can live with that for now.

tgd- don't panic! I assume everything is brand new? First make sure the chuck is "on" clean. 3-jaw chuck, you will have some run out. You are not looking at some real precision equipment here. If the chuck runs good, than I would say the jaws are not very good, but with a three jaw you can easy have .004 run out. Try re-clamping a few times with an indicator along side. Also a slight tap with a piece of lead or copper could help. How far out are you cutting? Let me tell you that even with a precision 6jaw you will have problems holding within .001 TIR. I think you are asking to much from what you have got.
As far as using "Master Jaws" and than boring out soft jaws to get more accuracy-forget it. Those are mostly used to .hold "special sizes". You will NOT repeat within .001. To do this right you will need a lot more experience. Save you money.

I assume everything is brand new?

actually it was used but the hour counter said 10 hrs when i got it and now it says 30

You are not looking at some real precision equipment here

the 3 jaw or the lathe in general?

How far out are you cutting?

typically about 4"-6" using a center. but when i am taking the measurements i am about 1" from the jaws.

I think you are asking to much from what you have got.

when i was saying .001 maybe that was a slight exaggeration maybe more like .005 if i need .001 i typically just use a file. but what your saying is if i really need .001 i am going to have to use the 4 jaw (already have one never used one but the lathe came with it) and indicate it to center.

Well thanks for the help.

[tjd10684]

While im at it here I want to make sure that my tail stock is properly aligned. so knowing that my chuck has an alignment issue i removed the chuck inserted a mt5 to mt3 adapter into the head. i then measured the run out the needle did not move so i inserted the mt3 to drill chuck adapter again measured run out needle did not move. i added the drill chuck and a piece of 3/8" precision ground stock locked it down and measured run out .00025. i then preceded to take my TDI and chuck it into the drill chuck adapter with the appropriate connectors. i then took the tail stock all the way in and measured around the inside bore of the tail stock and adjusted it until it read evenly though 270deg (i cant read the bottom). then i extended the tail stock to max and remeasured. it was off .0015 vertically, that is not bad (i think). so i break all this down put the 3 jaw back on indicate it to .0025. throw a peice of .750 aluminum in there and made a cut 6" long to check if i was making a taper. at the end closest to the chuck i measured .680 at the end near the live center i was at .675 not too terrible it works for my application but i know it could be better. did all that sound like a reasonable procedure for checking tail stock alignment or is their a better way.

[Davo J]

Hi,
What I do with my 3 jaw chucks is to machine the register on the back plate down a thou or 2 so the chuck can be positioned for the stock to run true.
Then you place a bit of true stock in the chuck slightly loosen the bolts holding the chuck, place a dial indicator onto the stock and tap it until it runs true then tighten the bolts. Depending on how good the scroll is it may or may not be true at other diameters unless you do this procedure for there diameter. I find with mine it runs pretty true at all diameters after setting it up for one, but if I am doing a repetitious job that needs to be accurate I will set it for that specific diameter.
A lot of guys use this method and usually call it tap true instead of set true. LOL There are chucks and bake plates that can be bought with adjusting screws built in to do this same thing but are usually expensive.

With your tail stock a DTI is no good for checking the vertical alignment of you tail stock the way you are because of gravity.
These are some pictures from a thread on HSM and show the effects of gravity.




To check if the tail stock quill is true to the ways place a mag base on the saddle with a dial indicator touching the top of the tail stock quill, and then run the saddle left to right and it will tell you if your quill is true to the ways.

To check if the tail stock is in line with the head stock spindle frank ford has one simple test
HomeShopTech
There is also a few threads over on HSM that goes into this. Aligning Tailstock - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

Centering Tail Stock Quill ????????? - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

The tail stock is usually set a thou high from factory to allow for wear over the years. Grizzly do make a gun smith lathe that has a torque wrench for the tail stock lock to bring it into perfect alignment when done up.

One thing that can vary your results over the length of the lathe is leveling. The lathe doesn't need to be level, just check that it doesn't have any twist in it from one end to the other. You can pick up a cheap 0.0005ft level for around $60 from a few places over their.

Dave

[tjd10684]

i would not have thought that gravity would be that much of an issue. but i do like the idea of cutting the stock and feeling it into place.

as for the chuck i dont think i can do what your describing. the chuck is a D1-3 with no back plate. i see the advantage if i were using a plain back chuck and an adapter plate but in this case the chuck is "bolted" directly to the head with locating pins. i tried different combinations of tightening to maybe get a different outcome but it did not really change anything.

Anyhow thanks for the rest of the info Ill check it out when i get home (writing at work)

[Delw]

If you have 2 pcs master jaws, buy a set up alum jaws and cut them to size for parts you want to hold accurately. softjaws will hold .0005 or better even on most worn out chucks.(unless really bad)
dont forget you need to locate/use a round spider in order to cut your jaws.
if you dont have a 2pcs master jaws than buy a chuck for the machine that has 2 pcs masters. you dont have to buy a very expensive one just a decent quality one. Bison works well.