Pm1340gt Cross Slide Lock Mod For Dro Machines

[mksj]

One of the issues when adding a DRO scale to the cross slide is that it often blocks the ability to use the lock. On the PM1340GT, they use a 6mm Allen screw on the right side of the cross slide which is completely inaccessible with the mounted DRO scale. I considered various options, but I wanted something (simple) that would securely lock the cross slide with no movement while machining with the Y axis. I ended up using the mounting holes for the steady rest to mount a 1/4" steel plate to the left side of the carriage, and it extends up to just below the top of the cross slide as seen in the picture. The plate is mounted with two 8mm cap screws.

The friction lock has an overall length of 0.8", so it has very minimal interference and the lock arm can be located down out of the way. I cut the lock body from 3/4" high strength 544 bronze rod (will not damage the steel), with 0.50" turned down and threaded to 9/16-18. The lock arm is 0.200 steel rod with a 8-32 thread on one end, it protrudes 1.125" from the lock body (any longer and they will interfere with the steel plate mounting bolts). When mounting the lock, I use a rubber washer on either side of the plate to give some friction (holds the arm when not engaged) and prevents chips from getting between the lock and cross slide. Once locked down, the X axis DRO stays within +/- 0.0001", good enough for me.

 

[wrmiller]

Very nice. I too have been contemplating a cross slide lock. Haven't decided on a design yet, but I've a couple of ideas. One is very similar to yours, but I'm hesitant about reaching down for that lock when I'm working close to the chuck.

EDIT: Oh...and you keep putting pics of that darn 5c collet chuck of yours and I may just have to go out and buy one. Stop that.

 

[jds]

I guess I screwed up, I ended up mounting my dro scale to the left side of the cross slide, so that I could use the lock.

 

[wrmiller]

You only screwed up if you ever need to use your follow rest as that mounts on the chuck side of your cross slide.

 

[tmarks11]

To the OP: nice job, that is a work of art. A lot of people just live with the loss of the cross-slide lock (which I would hate)... have to file this one away for "things to do" after I add a dro.

I guess I screwed up, I ended up mounting my dro scale to the left side of the cross slide, so that I could use the lock.

You did what a lot of people did. I would hate to give up the cross slide lock.

The down side of mounting the scales on the left side is they are in the line of fire of chips while cutting, although hopefully the shield mounted over the scale will keep the chips out.

My follow rest holds a treasured spot in a shelf somewhere, where I suspect it will always remain (unused).

Oh...and you keep putting pics of that darn 5c collet chuck of yours and I may just have to go out and buy one. Stop that.

Make sure you consider total cost of ownership. Bison 5c chuck: $600. Complete 5c collet set: $500-$1200. Making do with a set with 1/4", 1/8", or 1/16" steps can be an exercise in frustration. You gotta jump for the gold: 1/64" steps (69 collets to cover up to 1-1/8").

Full disclosure: I just live with the frustration...

But just to try to tip you over the cliff, here is my Bison 5" 5C chuck. Nice size, lightweight, easy to install. Grizzly has the best price I have seen for the direct mount D1-4 or D1-5 chucks.

 

[mksj]

Mounting the DRO scale on the left side gives you a little less clearance for large projects and more risk of contamination of the scale from chips/coolant. With the lock, I uses some sheet neoprene between the mounting plate and the cross slide, otherwise it gets gunked up with chips. Bill, you could also mount a friction lock on the back left carriage leg with a L bracket.

Agree wit Tmarks on the 5C collet set, started with 1/16th set and then had to back fill to 1/64th increments at considerable additional expense. Would have been best to have purchase a full 1/64th set from the start. Wanted a Bison, but at 3x the price it was hard to swallow. Littlemachineshop.com has an inexpensive set-tru type that works fine, although the body is not machined very well.

Threading the bronze rod to a 0.000 point initially set on the DRO. The proximity sensor hits the mark at the end of the cut (and stayed within 0.0002" on repeat cuts, amazing and easy), but you can see that the x-axis moves a bit through the process (about 0.0044"), so reason for the X axis lock.

 

[wrmiller]

Wow Tim, thanks for the eye-opener. I'll consider getting a er32 or 40 collet chuck set and making a adapter with a 1.5" through hole so I can just chuck it in the PBA set-tru when I want to use collets.

OP: sorry for the hijack. And after giving it some more thought, I think I've used a follow rest once in 20 years. I may just go ahead and do something similar and make it removable 'just in case'. Or move my scale to the chuck side and do a similar gizmo like I did for the compound, but that is a more permanent solution IMO and I would be unlikely to remove the scale to use the follow rest. Choices...

EDIT: mksj, just saw your reply post. Yes, I have also been toying with the idea of a friction lock mounted on the left front of the carriage.

 

[tmarks11]

Wow Tim, thanks for the eye-opener. I'll consider getting a er32 or 40 collet chuck set and making a adapter with a 1.5" through hole so I can just chuck it in the PBA set-tru when I want to use collets.

Good point. Requires quite a few more 5C collets to cover the range of 0-1" than it does ER collets.

5C collets requires your workpiece to be within +0.002" and -0.005" of the collet size, so even with 1/64" collet set, the collets don't overlap completely (since each collet is 0.016" off from the previous step diameter). Trying to jam workpieces of too large (or two small) a diameter risks damage to the collet and (in both cases) results in much less gripping force on the workpiece.

ER is more flexible, with allowed range of 1 mm (so within +0, -0.040" of nominal). I suspect it has less gripping force than 5C based upon the length of the collet, but have never read that anywhere. The downside is that it takes more force to tighten the collets, and takes longer to swap out collets (and you can't use a collet closer on them).

Wish I could afford to buy a 3J chuck system. But they make 5C look cheap!

The proximity sensor hits the mark at the end of the cut (and stayed within 0.0002" on repeat cuts, amazing and easy)...

Wow, that is an awesome mod. I will add that to my list when I do a VFD conversion.

 

[mksj]

I use an ER32 set-up on my mill, I would expect it probably has more clamping force then most other collets systems since the whole collet is in contact (~2") and collapses against the rod/drill, a 5C only compress at the tip and the contact area is maybe 1/4-1/2". Changing collets is much quicker than an R8 and 5C without a collet closure system, but you need two good size wrenches. A major limitation with ER32 is the largest collet is around 13/16", and if you where to bore a hole in a straight shank collet holder it would be under 3/4". An ER40 goes to 26mm, so would be comparable to a 5C in range, most people buy the metric collet set in 1 mm increments, which covers the 0.040" overlap. I had considered the ER40 straight shank chuck/collets for lathe and not switching out the chuck, but for now will try the 5C system. I plan to use use a 5C collet block set in the chuck if I need to do a single part and I do not want to switch out the 60lB+ chucks.

Precision C32 ER40 100L Straight Shank collet chuck holder 32mm diameter shank

 

[Rich V]

If you use ER collets I highly recommend the use of ball bearing closer nuts. They greatly reduce the amount of force needed to clamp down the collets.
https://www.maritool.com/Tool-Holde...437/ER32-BEARING-COLLET-NUT/product_info.html