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skipd1
07-18-2012, 05:14 PM
I am looking at adding a 3 jaw 6" Set-tru chuck for my lathe. I am not exactly sure how it adjusts concentricity and I am wondering if it is a good addition for more presise work holding than my existing 3 jaw chuck. What kind of accuracy can I expect and what are the better brands to look for? Thanks

Regards
Skipd1

tdmidget
07-18-2012, 05:22 PM
It adjust by moving the chuck on the mounting plate by pushing it with screws. As for as how accurate it is , I'm not sure what you are asking. Are you expecting to adjust it once and every thing there after will be perfect? Ain't gonna happen. I worked on a shop where we indicated parts to .0002 on them. Takes a bit of time but it can be done. The best are Bison, Buck, and Pratt-Bernard.

oxford
07-18-2012, 05:57 PM
I always thought that the benefit of the adjust tru 3 jaw was for production runs. You would set it true for the diameter piece you were putting in and then it would repeat for each piece with the same diameter. When going to a different diameter you would need to set it again.

The the OP, it sounds like you might just need a 4 jaw chuck.

tdmidget
07-18-2012, 06:15 PM
I always thought that the benefit of the adjust tru 3 jaw was for production runs. You would set it true for the diameter piece you were putting in and then it would repeat for each piece with the same diameter. When going to a different diameter you would need to set it again.

The the OP, it sounds like you might just need a 4 jaw chuck.
Setting it for a specific diameter would be better than the typical 3 jaw but if you are working to less than .001 you will have to indicate each part. The advantage over the 4 jaw is that you have less distortion of the workpiece as the force on each jaw is the same. It is VERY difficult to indicate a hollow part to tenths on a 4 jaw with out distorting the part. If it is really critical then a 6 jaw is the way to go.

oldtiffie
07-18-2012, 08:59 PM
Why not use a 3-jaw chuck with "soft jaws" (machined to suit a part) as its about as near to collets and their accuracy as you will get.

My "3-jaw "tap-true"" is about 0.003>0.005" clearance between the chuck backing plate spigot and the chuck rear face locationg recess. I just use the back-plate to lathe flange screws to make the adjustment - loosen the screws to a light "grip", tap the job (in the 3-jaw chuck) with a dead-blow hammer (or similar), and when "true" just tighten up and re-check. If OK you are set to go - other wise repeat the process.

Forrest Addy
07-18-2012, 09:39 PM
Do I rant about 4 jaw chucks now? Or later?

oldtiffie
07-18-2012, 09:48 PM
Go for it.

http://en.wiktionary.org/wiki/rant

TexasTurnado
07-18-2012, 10:09 PM
Do I rant about 4 jaw chucks now? Or later?

Go right ahead, Forrest.... I was not aware anyone needed permission for a good rant....:D

flylo
07-18-2012, 10:15 PM
Go to http://buckchuckusa.com/. They claim .0005" tir repeatability. This is on my Pacemaker. Looks likes the best if both worlds to me.

oldtiffie
07-18-2012, 10:27 PM
I am looking at adding a 3 jaw 6" Set-tru chuck for my lathe. I am not exactly sure how it adjusts concentricity and I am wondering if it is a good addition for more presise work holding than my existing 3 jaw chuck. What kind of accuracy can I expect and what are the better brands to look for? Thanks

Regards
Skipd1

First of all, it would be assist to narrow the search if you nominated the degree of accuracy that you need.

For short-run stuff at best and quickest setting-up accuracy I'd nominate a 4-jaw chuck followed by a 3-jaw chuck with "soft jaws".

That way I can use what is in the shop at no or minimal additional additioal expense - or delivery-time delay.

lakeside53
07-18-2012, 10:47 PM
Don't sweat the naysayers. If you want a 3 jaw set tru, go for it.

I have a Bison and love it. I also love my Rohm 4 jaw comination set and scroll. Soft jaws are fine, but often it's easier to just adjust the set tru and get on with machining.

tdmidget
07-18-2012, 11:13 PM
Do I rant about 4 jaw chucks now? Or later?
You might not remember, Forrest, but I've met you and I know you're good. But can you put a 2' OD, 1.75 ID piece in a 4 jaw and indicate to .0002 without more than .0002 distortion? Don't think so. I've had to to do it several hundred times, with 6 jaw Buck and Bison chucks. Ain't easy.

moe1942
07-19-2012, 11:33 AM
Make your own.. Easy task.

tmc_31
07-19-2012, 12:13 PM
skipd1,

First of all let me say that for most of the precise work that I do on my lathe (which is not much), I use a 4 jaw chuck. Thanks to some encouragement and instruction from Forrest and some others a few years ago, I learned how to dial in my 4 jaw to within .001 or better quickly and consistently.

That said, most of the work I do, does not require that kind of precision. While +/- .005 is usually good enough, I prefer to get to +/- .002 or better. I was having a terrible time achieving this with the 3 jaw chuck that came with my lathe and using a 4 jaw was just two slow and tedious in a production environment . So I went looking for a adjust-a-true chuck that I could afford. Another problem I was having was that the work was spinning in my 6" 3 jaw chuck (bad juju when you are power tapping in the lathe). I finally settled on a Gator (Fuerda) 8" 3 jaw adjustable chuck which I purchased from Jeff Beck at tools4cheap. For my needs, this chuck has been excellent. I have not used a Buck or a Bison chuck so I have no point of comparison but I am very happy with the Gator that I got. Also Jeff is a nice fellow and is very helpful in selecting the chuck that will meet your needs.

All the best,

Tim

Bob Fisher
07-19-2012, 01:44 PM
The only time I worry about my chuck is a 2nd operation. I try to plan to turn everything I can in one chucking. No problem with Run out. If it's a one off, use the 4jaw,if there's multiples, go with the soft jaw approach. Again, most of the stuff I do does not require all that much accuracy, but I don't know how I could live without a lathe of some sort. A simple little bushing,would have most people headed to the hardware store, where we head to the lathe and make an even better replacement. Bob.

Kernbigo
07-26-2012, 07:01 PM
make your 3 jaw ajustable like a buck it is not that hard to do, turn your back plate -.010 and put 4 adjusting screws in your chuck like a buck, mine will hold .0005 Kernbigo

tdmidget
07-26-2012, 08:17 PM
Are you saying that it will repeat to that at a particular size? Or that you can indicate to that? Big ddifference.

Kernbigo
07-26-2012, 08:45 PM
mine will repeat to that size with in .0005 and a different size probaly with in .001, mine chuck is a cushman, work great, even a buck you change to greater range and it will go out more than the .0005 that you indicate to

JoeLee
07-27-2012, 11:38 AM
I have an 8" Bison 6 jaw set true. I can get it to repeat with in 2 or 3 tenths if....... I use a ground piece of stock of the same size and tighten the chuck up with the pinion that is marked "0". Put a larger or smaller dia. piece of ground stock in the chuck and I usually won't get the same repeating results, but it will be with in .005. Try it with a piece of CR round and for get it. As the scroll and jaws wear the repeatability will change.

JL.............

Rosco-P
07-27-2012, 12:35 PM
For the repeatability you are expecting on a multiple parts run: soft jaws or an ER collet bored out.