Quill DRO for a PM935?

[Alan H.]

"WARNING"
Follow-up on the installation I did -

I did not get the mounting screws for the Mitutoyo mounting bar short enough. The mounting bar uses the same holes as the factory depth scale for installation. The factory scale is mounted over the Auto Feed mechanism (see pg 14 of the PM manual). While I did not believe the bottom screw was interfering with the trip push rod that locks the "Quill Auto Feed Lever", turned out that it actually was interfering just enough to cause a problem.

While everything appeared to be fine, the screw was just long enough to bind the "Trip Push Rod" itself and the "Quill Auto Feed Lever" would not lock and hold position. Lesson learned - Make sure that screw is short enough that it will not infringe onto the trip push rod.

As always, Matt at QMT was ready and willing to help but it turns out that I had laid a trap for the both of us and I wasted Matt's time. Sorry Matt!

Trip Push Rod schematic:


Here's a photo of the mounting bar in place with the two screws in the original attachment points for the factory depth scale. Size the length of this screw to not interfere with the function of the Trip Push Rod (#5 in schematic above):

 

[[X]Outlaw]

Thanks for posting this! I'm picking up my DRO kit tomorrow and hoping to install it over the weekend. Between Abom79 video and this thread I think all the "gotchas" are well covered.

 

[petertha]

Apologies, I posted elsewhere on 935 quill DRO & then found this post specific to the Mitutoyo model 053906 (sometimes B on end?).
I'm relatively sold on the Mitutoyo, mostly because it happens to be on sale right now! But I've noticed I have not seen a picture of the DRO in conjunction with the down feed hand wheel. Is that because people just don't use the hand wheel much, or the DRO conflicts with it?

 

[[X]Outlaw]

I don't have a pic right now but the DRO in no way conflicts with the handwheel.

 

[davidpbest]

The Mitutoyo Quill kit is ok, it works, doesn't impinge on the downfeed crank-handle. That said, I prefer to make my own mounting brackets, which you've probably already seen ( LOL ): https://flic.kr/s/aHsmpXogeF

 

[petertha]

...which you've probably already seen...
Oh-Ya!
David, with your integrated set screw micro-adjusters, does it lend itself to running a test indicator up the face & edge of Mitutoyo scale on quill movement, kind of like dialing in your XYZ DRO scales? Or is it mostly about dealing with casting variations & geometry in general? Any general words of wisdom re drilling & tapping cast iron for bracket items like this?

 

[davidpbest]

Peter, please realize that the primary reason I ditched the Mitutoyo supplied quill mounting bracket system is because I needed to integrate a proximity sensor into the quill DRO encoder mounting system. This proximity sensor triggers an auto-reverse when the sensor detects the quill stop, and is handy for threading operations. Thank you Mark Jacobs.

If I had not needed to add the proximity sensor, I might have used the Mitutoyo supplied bracket system, modified along the lines of what Alan H did.

If you do decide to make your own brackets, here are some tips. First, be very careful where and how deep you drill and tap the head casting for mounting screws. You're working in an area where the power downfeed trip mechanisms are buried inside the casting. See this for more info: https://flic.kr/s/aHsmq2F8fj

The other thing is that if the Mitutoyo scale is not precisely aligned and kept flat, the encoder part (which is attached to the traveling doughnut ring) will drag on the scale enough to add friction to the quill movement, defeating the auto-retract spring no matter how much you tension the retract spring. That was the purpose of the jacking set screws in my bracket design - to be able to tweak the angle and casting offset for each scale end.

There is no practical way to check the alignment of the scale part using an indicator or similar - it's a matter of fussy trial and error, and to get all the friction of the Mitutoyo DRO dialed out of the system, it took me a couple of hours tweaking things. Since I didn't install the Mitutoyo bracket, I have no idea if it's easy or fussy in this regard.

Hope this helps.

 

[Boxster9]

David your projects are always a joy to behold. Thanks for sharing your thoughtfully and well engineered ideas. Coupled with the magic of Mark Jacobs and its Wow! You both deserve a heartfelt thanks for sharing and enlightening the rest of us.

 

[petertha]

OK, here goes with my installation. I will preface this by saying - what a weird piece of kit! Kind of a puzzling assortment of hardware & bits of pieces with no clear instructions as to what they are for. Unlike the proverbial Ikea furniture build, I had hardware left over! Recognize there may be variations to '935' mills out there. Also I am no expert. I'll run it this way for a while & if I see things I don't like, I'll report back.

 

[petertha]

My stock rule scale was removed & exposed M4 screws & threaded holes in the casting. Similar to others, my screws did not have sufficient clearance in the slot so cleaned up the aluminum bar with 4mm end mill. Found center & took off about .007" on either side, just enough to give the shank clearance. It wasn't just anodizing buildup, the slot itself wasn't cut so great.

I measure how much the stock screws protruded into the casting & ended up using M4x10mm cap screws to give me the same penetration. Someone pointed out if the lower one goes in too deep, it can mess up the down feed mechanism. Thanks for that heads up!