New PM-728V-T Mill

I have a PM728T that was delivered in June (if I remember the date). The reason I got it is for CNC conversion. I also purchased a PM1022 lathe around the same time, also for CNC conversion. The lathe was delayed and finally delivered Sept. 8. My plan was to do these conversions over the summer. A lot of work to be done so I ordered a PM CNC conversion kit for the PM 728 to speed that one up! If the kit doesn't become available soon I'll likely cancel that order and do my own conversion. Last I heard, these kits are due out sometime in Oct.

I'm working towards the PM1022 conversion. The available space for a conversion look a lot tighter than for the 728. It is starting to look possible though.

jimrk: You are doing a very nice job on your 728 conversion. It's the first conversion I've seen come to fruition. It seems to be moving along rapidly in my estimation. Congratulations. If I may, I'd like to ask a few questions. First, is there any possibility of getting drawings/sketches of yours? Did you use 2005 double nut ball screws on all three axes? Did you have to move the lead screw axes or are they in line with the stock screws, i.e. could you have used the stock end plates? You mentioned the Clearpath stepper motor used for Z above. Did you use the same spec motors for the X and Y? Thank you for any info you can provide.

If I do the conversion myself my current thinking is to use fairly short NEMA 34 steppers for X and Y. Mount these towards/under the machine, rather than sticking out, with a timing belt drive. For my application space is absolutely critical. For electronics likely LinuxCNC, Mesa cards, and Gecko stepper drivers.

Glad I found some CNC content in this thread. Thanks.

Hugh

jimrk said:
Plugging away a bit at a time.
Click to expand...
 
Have been slowed down by Wild Fires in my area. We were VERY lucky and had no damage but were evacuated. Have a Power Draw Bar sorta working. Tormach R8 holder on order.
 
That is awesome! Can you provide some more detail on how this works? I assume there is a spring holding the drawbar up tight and the cylinder pushes down on the drawbar against the srping? How much pre-load does the spring provide?
Also, I don't know if you noticed but the entire assembly lifted off the mill in that video! You better tighten something!
Robert

Edit: Sorry, I see now that it is spring loaded so it can lift up. Why was that necessary? Couldn't you just shorten the stroke? I wonder if you could do this with a linear stepper rather than an air cylinder?
Robert
 
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There are plenty of examples of how this works. Hoss might have been one of the early ones. Priest tools has good vids as does Sam (CNC4XR7)


Belview washers are used to hold the tool holder in the R8 collet, then the air cylinder pushes between the draw bar and a plate to compress them more. Like unscrewing the drawbar with no forces on the spindle bearings
 
OK! Thank you. that video was very illustrative. I have never understood these in the past. I see now that the objective is to avoid putting force on the spindle bearings. I also see that the forces required would exceed what could be provided by a linear actuator. I have some ideas on this however!
I would have thought that the spindle bearings could handle this downforce?
Robert
 
Made the tophat out of aluminum for testing. Added a steel collar to keep the new drawbar centered.
tophat.jpg


encoder will be in the front somehow
pdbth.jpg
 
Working on the encoder mount. Used a PDB plate that had an oops. Hole was correct size to fit the encoder so reuse it. Liking the Super glue trick for fixturing.

Cut slots in the side plates for it to slide in and out with a set screw to keep it in place.

encoder mount.jpg
 
Jimrc- What is the plan/need for the encoder? Do you need the spindle position for threading or some other operation?
Robert
 
Correct, along with speeds & feeds. It's easy with the Acorn board so might as well.
 
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