Help with boring out lathe jaws...

I bored out some jaws on a cnc lathe, and my bar runs out .004 approx.
Iv'e bored out tons of em on a manual dead nuts every time.??
After looking at the manual lathe I realized a difference, The manual lathe has jaws behind the jaws, and they are obviously a bigger diameter than the bolt on jaws. So dropping in a round piece in there works fine. But the cnc lathe has no back jaw. Nothing. So I clamped on the area "on the bolt on jaw" that is a clearance area behind the jaw. It's only about .2 long or shorter, real hard to get something square in there to hold the jaws open.
I gotta be doing this wrong.
Anybody mastered this wanna help out an apprentice?
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vinny wrote:

Vinny, Were you boring all the way through or just a step in the jaws. If your going all the way through putting pins in the bolt holes and then clamping a disc with a large hole in it using the pins in the bolt holes might help your problem.
US Shoptools offers this gizmo that works in a similar fashion:
http://www.usshoptools.com/current_year/all_products/2010_11_pdf/PGS_10.pdf
I've used the one that is at the top of the page and It's worked well for me.
Also I set the chuck pressure at the pressure that I want to run at and don't change it after boring out the jaws.
Best, Steve
--


Regards,
Steve Saling
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Thanks for the link, im buying one today.
As far as chuck pressure...I'm clueless. The words over the air gage says something like max air blah blah blah 25 metric. someshit/cm bla blah But the gage is in bars/foot lbs. The last time I ran one I could of sworn I used a max number of 400 lbs. I'm at like 280lbs now?? For a 1.5" solid piece sticking out of the chuck 2-21/2 inches. I clamped on the edge of the bar, say .100 or less and it left a mark. So I backed off till it left no mark. Tell me that isn't just sad lol Just ran a 40 piece job and the bar didnt come loose. WHAHOOOO!!!!
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Just watched a youtube video where some guy went thru everything with a camera. His haas lathe said on the side: 200 for normal lathing 160 for collets 500 max. And it was in the same measurement system as the one im on. Same size chuck. At least I got something to go by now.
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I ran into trouble once on a real long part that needed extra tall soft jaws. clamping like you do, left the part loose at the end of the softjaws. So, I built a plate on my cnc mill with sets of 1/4" spiral slots, each set of three 120 degrees apart. Enough sets to do almost every diameter.
Then just drill and tap 1/4 20 in the top of the softjaws, line up the plate, put in three bolts and tighten chuck. Now the holding force is at the outside edge of the softjaw.
It took a long time to make my plate, but this works WAY better than looking for the right piece of scrap.
Karl

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Manual chucks have a scroll to operate the jaws and out of the 3 key holes one is marked. Thats the one to use for the most repeatability. CNC style chucks use a draw tube to push and pull a wedgey type mechanism to open and close the chuck. Your repeatability will be based on the looseness of that fit. If your wedgey mechanism is loose you can bore the jaws out with spiders (either a piece of round stock to clamp while boring or a washer to bore through while boring) all you want and you will still get run out. Watch the chuck when it closes onto the stock. Loose chucks "oversqueeze". You can see the whole jaw assembly push out while the jaw has more pressure in the back than the front. You can overcome this by boring some negative taper into your jaws. How much taper will depend how loose your chuck is. The best way to solve your run out issue is a brand new chuck.

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It's a new chuck that came with the lathe...doesnt mean its good though. I bought a lathe monkey for the chuck, I'm hoping this is all I need.
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Its a crap shoot with hydraulic chucks some are tight and repeat all day, some never repeat.
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That's good to know, because all presume a new cnc lathe chuck will have perfect tir.
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Are the faces removable? If so takem over to the mill & cut a step in the back so you can get a min 1/4" disk behind the bore. A little calculation so you can use a standard ring (commercially available in sets) The jaws should be bored close to the fit of the work piece, otherwise when you open or close the scroll is in a different area & does not repeat.
--
~g~

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wrote:

Are the faces removable? If so takem over to the mill & cut a step in the back so you can get a min 1/4" disk behind the bore. A little calculation so you can use a standard ring (commercially available in sets) The jaws should be bored close to the fit of the work piece, otherwise when you open or close the scroll is in a different area & does not repeat.
****** Tommorrow I got to bore out some blind pockets. I'm gonna try these drills that you can turn with also. Drill down the middle, then using the same tool bore it out. No center drill needed. The bores are like an inch or bigger diameter. The drill is 3/8 maybe. Maybe an inch or so deep. Thing is, do I go maybe .5 deep and bore out to size, then drill 1. then bore out, etc... Or, drill to depth then bore to depth. no coolant thru drills, but an inch isnt so deep, even in stainless. ?
This time I can put a nice piece of stock in the jaws since my part is only an inch long. I dont have to bore thru. My plan is to start with a round piece the same diameter as the one im cutting. It will be lathed, so it should be pretty round. Clamping on 3/4 or more of an inch of jaws for the bore of the jaws. I'll touch off the boring bar and bore the jaws exactly to size. Hmmmm, I wonder if RPM matters? High rpm makes the jaws hold less, I wonder if that would effect tir?
Anyway, this will be a test of how good the chuck tir is.
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Being a 1st time with your "drill-bore" tool , nice & S L O W. <g> I've used those in the past, but finish bore should have been done with a single point bar- a minor dia. for threading tool. If it was'nt roughed out with the flat bottom drill - right - the threading tool crashed.
Those pilotless drills are sweet but they wobble a bit till fully engaged - make nosie like hell. thats nice you can take a bore cut after plunging. Who makes that tool?
That noise! must be Vinny roughing shit out! sqweeeeeeeeeeeeeeeek!
Hey a noisy shop is a productive shop.
--
~g~

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wrote:

Being a 1st time with your "drill-bore" tool , nice & S L O W. <g> I've used those in the past, but finish bore should have been done with a single point bar- a minor dia. for threading tool. If it was'nt roughed out with the flat bottom drill - right - the threading tool crashed.
Those pilotless drills are sweet but they wobble a bit till fully engaged - make nosie like hell. thats nice you can take a bore cut after plunging. Who makes that tool?
That noise! must be Vinny roughing shit out! sqweeeeeeeeeeeeeeeek!
Hey a noisy shop is a productive shop.
*********
Today, I got it all programmed up in mastercam, dry ran it, looked sweet. I then hit go, it came over, and fed into the part and snapped quietly and quickly.
Why? not sure yet. Who knows if the lathe is even on center, it's supposedly set at the factory, but who knows? I'm prolly just gonna use drills and a boring bar.
One question...do people bore with the spindle running the same way as it does when facing/turning? The reason I ask is mastercam seems to want it the opposite. Maybe I'm running the boring tool upside down making mastercam harder than it really is?
Frig, not even one lathe example in the help files for boring a hole. Jeesh.
Sorry this post was so "boring". lol
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vinny wrote:

Did you look at the X offset, maybe a boring bar was used and the X offset was something other than zero?

Yes
Best, Steve
--


Regards,
Steve Saling
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When I left today I noticed I had .315 in the x offset for that tool. I'm about 70% sure that's what happened. DOH!
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Damn I hate that .315 offset!
************
THATS IT MAN! The friggen tool was .315 diameter! I had to of picked it up in X. I would of done that because its a drill AND a boring bar. so... Now the question is how to deal with drill/turn tools?
I suppose I could put that x offset in the next tool slot, then when programming, call up the next offset instead when doing the boring.
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