June 13, 2017 at 3:35 pm #3293
I’m having issues getting level girdles and I think the problem may be a bent quill (MDR 300-C faceting machine). Might be technique too of course. The alignment per the manual is fine.
To check the quill rotation I set the angle to 90 (actually just under to guarantee a single point of contact) and touch the dop to a master lap. Then I rotate the dop through 1 revolution and watch the dial indicator. The dial indicator varies 0.001″ (from high to low) as I rotate the quill though one revolution. The dial indicator touches the stop arm 1″ from the pivot and the dop touches the lap 5″ from the pivot. This implies a 0.005″ error at the dop.
This isn’t huge but it isn’t zero and is the largest error in alignment I can measure. How big an error is too big and should I try to find the error?
CharlieJuly 13, 2017 at 2:52 pm #3371
Wow, still no reply. Does anybody have the ability to provide either an angle difference or dial gauge difference as they rotate their faceting head through one rotation?
I’d be very curious how large a value you see.
CharlieJuly 13, 2017 at 4:02 pm #3372
Odd that your “no reply” message is timestamped an hour before the original question.
Not many people are familiar with the MDR, so you may not get much helpful advice. I would first make sure that it’s not a problem with the dop. Rotate the dop 180 degrees in the quill and see if you get the same measurements. I don’t know how the dial indicator works on that machine. Most indicators measure angle, not distance.
Anyway, good luck, I hope someone familiar with the machine can answer.July 14, 2017 at 3:35 pm #3378
Strange about the timestamp. I made the original post on Jun 13th, a month earlier. Perhaps there’s a glitch with the forum software.
Anyway, WRT the underlying question. I’ve attached an image of the MDR head. The dark colored knurled knob on the left allows you to set the angle. The silver knurled knob at the bottom sets a hard stop. Next to that you can see the point for the dial indicator. The distance from the pivot (silver nut on the black axel left of the label is roughly 1/5th the distance from the pivot to the end of a dop. To make the measurements I provided in the original post I put an empty dop in the collet and measured the offset with the dial indicator as I moved around the index gear on the quill. I listed the maximum offsets. With a little trig it’s easy enough to calculate the angular difference for that. If my math is correct the reported error would be approximately 0.06 degrees.
I’d love to hear either equivalent distance errors or angular errors (easy on an Ultra-Tec or similar) so I can make a comparison.
Thanks in advance.
Attachments:You must be logged in to view attached files.July 14, 2017 at 5:12 pm #3381
The problem is actually failing eyesight, I think. I can’t tell the difference between June 13 and July 13 🙂 Mystery solved, except I don’t know why I didn’t see the original post.
Thanks for the photo. I’ll have to study it a bit. On my Graves Mark 5XL, I do the equivalent measurement by laying the dop on a precision block and adjusting to 90.00 degrees. Then I rotate the quill and adjust the micrometer height adjustment until I get the same angle, so I get the difference in depth of cut directly from the micrometer. I repeat it by rotating only the dop, to make sure it’s straight. I did have a similar problem a while ago, but Peter Erdo from Graves fixed it quickly (and inexpensively). It’s now less than 0.001″.
BTW, precision 1-2-3 blocks are inexpensive and useful for a lot of things.November 2, 2018 at 6:23 pm #5047
i find it very funny with everyone trying to get exact degrees. very slight differences do little to change view-able brilliance. as long as you are in correct range, do as good as possible in matching your facets and get that as perfect as possible polish, your stone will be brilliant. all these ultra infinite fine reading and setting is just over kill, the eye can not see a sub fraction of a degree in a small object. people ow and aw at my stones and their not cut to those super infinite degrees and tolerances. and i don’t go for competition either, my egos not that runaway. and i’ve been cutting for 50 yrs and doing special cuts and stones for others too. as for your machine, i have 2 MDR’s one very old and one newer without the dial indicator. set to 90 on the stop and check the main quill shaft nere end for out of round, if good then check your dops. also check to see if you might have something in the whole where the dop goes. also there are Colet type and set screw type tightener to hold dop in. a bur indent in the colet type can throw of centering. and unless the whole for the dop and the dop are exact, normally not, so you can insert the dop, the set screw will push the dop to opposite side of whole– of center– got it. firstname.lastname@example.org
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