PM1340GT with a 3 jaw Pratt Burnerd 6" SETRITE

[mksj]

A consideration for individuals buying a new PM1340GT or similar lathe package is to consider including either a Bison Set-Tru, Pratt Burnerd SETRITE or even the something like the Grizzly or Shar's adjustable version's if on a budget. Note that some chucks are 6.31" (160mm) and some are 6" (152mm), so check all the specs.

The stock Taiwanese chuck that came with the PM1340GT is nicely machined, but mine had a TIR of 0.008" out of the box. A bit of tweaking and I was able to get this down to ~0.002" with a repeat reproducibility of ~0.003", which is about expected. There is variation, so some may be better or worse. A credit to the PM1340GT machining, the spindle nose TIR is almost unmeasurable at 0.0001".

So I decided to upgrade to a Set-Tru 6" three jaw chuck, they are also available in 2, 4 and 6 jaws to suit your needs. I narowed the choices down to the Bison Set-Tru and Pratt Burnerd SETRITE, mostly because I was looking for chucks with higher quality builds. The Buck, which is now made in Taiwan, was more expensive then either of these when you compared pricing with a backing plate. If you can afford it, buy once, as opposed to upgrading multiple times frm lesser quality. Normally I would have gone with the Bison version, but the Grizzly prices on both of the PB and Bison with a backing plate is very close. It is nice to see that Grizzly is carrying higher quality tooling, and I also noted that they carry Aloris and Dorian QCTP/holders at great pricing. I use a Dorian QCTP with Dorian and Aloris holders.

Anyway, so ordered the PB chuck with a D1-4 back plate from Grizzly, and got it fitted to the PM1340GT. The PB is nicely finished (although a few shipping dings), it uses uses a single pinion (Bison is 3) and comes with two piece jaws. Took about 30 minutes to adjust it, and the TIR is now ~0.0001" (see attached video file, resolution is 0.0001/division) with a repeat reproducibility of around 0.0003". Not that I can machine to those tolerances, with the previous chuck I had some problems hitting my target dimensions. Since I am a newbie at the lathe, having a bit tighter tooling tolerances seems help, and I appreciate good tools.

So, everything is a learning curve, and learning about good tooling is a process. The Set-Tru type lathe chuck was a pleasure to set-up and use. Definitely should be on the short list, I would give this consideration if you are looking at a packaged deal (including a chuck) when buying a new lathe.

 

[wrmiller]

I already have a PB on my list for my 1340GT.

 

[Coug67]

I'm a little confused. I have a 1340 on order myself, and I thought the spec said guaranteed .0001 runout. Is that just at the spindle bearing itself? You're saying (and I'm not disputing) the true runout was almost 80 times the listed spec. That seems excessive given the quality build that I keep seeing in the reviews on this lathe. I'm (almost) completely new to machining, so maybe that's a stupid question. I guess I assumed the runout was measured at the chuck nose with the supplied chuck. Could you enlighten someone who's still learning?

 

[mksj]

We are here to share and also learn, so never a stupid question. The spindle runout is 0.0001". The chuck mounts to the spindle and is locked on, the pm1340gt uses a D1-4 mount. The chucks come in various levels of quality and specs. There is also the repeatability of the setting. Most quality non Set-Tru or Setrite type chucks have a TIR spec of something like 0.002" or better, while Set-Tru type (which use small screws to allow microadjustment in centering the chuck) usually have a repeat TIR of something like 0.0004" for a 6" chuck. There are a number of factors that can influence the TIR. Some backing plates are fully machined, others require you to take a skim cut on your machine to true it up. Runout may also be positional, in particular a Set-Tru type, so use alignment marks so it always mounts in the same position.

My general comment, is that if you need a high level of accuracy and repeatability, I would invest in higher quality chucks up front if the budget allows. I ended up replacing all the stock chucks, which were very reasonable priced, but I needed better TIR and repeatability specs. I also look at this as an investment over many years of use. I did not appreciate the total $ amount required to properly tool the lathe, but it is a significant part of the total cost.

 

[wrmiller]

I have a Pratt 8" set-tru three jaw just waiting for me to finish setting up my 1340.

 

[tmarks11]

As long as you don't need to recheck your part, once you start turning the part down, a TIR of 0.005" on the 3 jaw chuck does't matter, as the TIR of the spindle is what matters.

But if you then remove the part from the three jaw, and re-chuck it, the next turning you do will not be concentric with the first cuts.

So unless you have a set-true (adjustable) style 3 jaw, you don't re-chuck with a 3 jaw. If you have to do a second cut in a different setup (like reverse the part in the chuck), you either use a 4 jaw (which you adjust to get 0 TIR on the part), or a 5C collet (which tends to be more accurate than most 3 jaws).

The Beauty of the set-true is that you CAN use it for re-chucking parts, since you can adjust it to get 0 TIR. Oh, and adjusting the set-true is 1000x easier (and considerably quicker) than zeroing a part in a normal 4 jaw.

 

[wrmiller]

The Beauty of the set-true is that you CAN use it for re-chucking parts, since you can adjust it to get 0 TIR. Oh, and adjusting the set-true is 1000x easier (and considerably quicker) than zeroing a part in a normal 4 jaw.

While I agree with you on this, I was told by some here that the opposite is true.

Probably just depends on who becomes familiar with what.

 

[tmarks11]

Longer to adjust with a set true?

1. Loosen the 4 holding cap headed bolts, than snug them up hand tight.
2. Back out the 4 adjustment screws
3. DTI on the chuck, spin it to the high point, use the opposite side screw and adjust it half way to 0
4. IMPORTANT: back that adjustment screw back out again (the snugged up holding cap screws keep the chuck positioned).
5. Repeat steps 3 & 4 until zeroed.
6. Tight the holding cap headed bolts.
7. hand snug the adjustment screws (don't tighten them up... they don't hold the chuck in position).

This should take no more than about 2 minutes. It is awesome.

The four jaw I can get zeroed in 3-4 minutes, but if you have an aluminum part, you have to be careful not to damage it, when you tend to want to crank down on one of the jaws to shift its position.

 

[wrmiller]

Relax dude, I said that I agree.

I can set a set-true in half the time or faster than I can a four jaw. But to be truthful I have more time on a set-true.

 

[coolidge]

Yes but...I found this process rather annoying on the Bison since the adjustment screws are not at 12, 3, 6, and 9 o-clock. So you get into loosening two and tightening two, back and forth, yeah I had to take a time out I was getting hot under the collar. That my CHINA test indicator was in the process of falling apart at the time may have been a contributing factor. Since replaced with a Mitutoyo. Bill are the adjustments screws on the Pratt Burnerd different?