Author Topic: My new faceting machine (a horror story)  (Read 654 times)


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My new faceting machine (a horror story)
« on: June 11, 2020, 06:28:40 PM »
Readers beware, this is a lengthy horror story....
Last year in te end of september I ordered a Polymetric scintillator 88.
I had read many good things on the internet about the machine and the customer service from Polymetric.
The machine was supposed to be ready for shipment in two to three months, in the end I waited over four and a half month for it to arrive.

When I plugged it in the motor was very noisy and vibrating very violently,
The whole machine was vibrating along with the motor, so much that when I looked at a stone with a loupe, I could just see the stone vibrate, and could not focus on the facets.
The digital readout was flickering at set points, and it was impossible to set the readout to certain angles.
44.1 degrees is impossible 44.7 then 47.1 and 47.7 etc etc, always the .1 and the .7 The readout will just flicker from 44,0 all the way up to 44,2
I contacted Zane from Polymetric about the issues but he could not really provide a solution, other than a few things to try.
I tried everything to fix the readout; grounding the machine, different power supply, but it did not help.
Then I found out that the motor controller output was 180 volt DC while the motor was only 90 volt DC.
Zane had to contact the factory from the controllers to get some answers.
I found 3 different manuals online for that model of controller, all saying different things about the settings for 90 V DC output.
I found out that there was a stepdown setting for the controller so it would supply the 90 volts instead of 180.
In the end it took a month for Zane to give me confirmation on which manual to follow, and how to set the controller.
I did the adaptation and the motor did run much smoother and made a bit less noise, it was a small inprovement.
The entire machine still vibrated way to much though.

At that point I doubted what to do with the situation; Send the machine back to the US or try to fix it and start cutting stones.
Sending it back was not really an option as shipping is already 400 euro and I had also paid over 1000 euro import taxes to dutch customs.
So I decided to try to fix the motor issues and make the best of it..... :'(

Zane told me he would try to find out what was causing the issues with the motor, but would have to contact his suppliers again.
I made brackets on the machine for the motor, I put acoustic foam between the brackets and the motor and did not bolt the motor down.
That way there was no metal to metal contact between the motor and the machine.
Then I made a motor cover and put acoustic foam on the inside of it.
The machine was less noisy this way and vibrated a lot less. It was still vibrating to much though so I attatched the machine to a 40 kilo aluminium base plate to try to reduce the vibrations. Its helped but the machine was still vibrating.

I decided it was good enough for now and I wanted to start cutting stones. (maybe Zane was going to send me a new controller that would fix the problems)
So I tried to put the drip tank on the machine but the hole in the drip tank was to small to fit the stand......
This was highly annoying because the hole should be 12,7 mm (1/2 inch) but they dont sell those size drill bits here in the Netherlands.
If you can find them then they are very expensive. It took me an hour and a lot of sandpaper to get it to fit.

I finally started cutting but I had issues with the angles of the mast. After setting the angle to 41 degrees it slowly shifted to 40.9 while cutting.
The screw for setting the angle had a lot of play and just slowly shifted, the course setting for the angle is also a bit dodgy; I have to tighten it like a madman so it does not drift and stays put.

Ok... so another attempt cutting a stone.....
New problems arrise cutting a row of facets; after a long time I find out that the height setting of the mast is also slowly shifting when cutting.
Set it to a certain height and it slowly moves down up to 0,2 mm. I also notice that the slide plate for the mast is not level, also at least 0,2 mm height difference.
I contact Zane again and he again gives me some tips and things to try, but it does not really help.
I try everything to adjust the mast so the height setting stays the same but I cannot get it fixed. The fine height adjustment knob also has a lot of issues!
It is not responsive; the height changes only after rotating the knob 90 degrees, yes a quadrant of play in the knob.
and I can feel that the cover plate is running into the mechanism for the fine height adjustment so half a turn is smooth and the other half is not.

I contacted two machinists that I know to get some advice on the machine and hopefully get it fixed.
They dont know each other but after looking at the machine they both say the exact same thing!
Why is the lead screw made of brass? (it is bending causing play in the height adjustment)
Why is there no bushing for the lead screw in the bottom like there is in the top?
Why is the lead screw 12,7 mm and the bushing has a 13 mm bore?
The lead screw runs through the facet head connecting with a little set screw but they both say that this mechanism is causing a lot of play in the height adjustment.

At This point I have had the machine for two months and have not cut a single stone.
By now I am pretty upset with the whole story and I contact Zane again.
He tells me he is going to send me a different controller soon that should eliminate the issues with the motor, but he has to test it first.
I request some compensation from him for all the problems with the machine, and he agrees to send me a different controller and compensate me with some goodies like index wheels or maybe a small financial compensation.

One of the machinists makes his own faceting machines and laps and offers to help me out and fix the machine for me.
So I bring him the machine and he contacts me a few days later saying that there is even more problems with it then I had thought.
The mast is not vertical, the slide plate for the mast is bend and not flat. The space between the lead screw and the mast is different at the top of the mast and at the bottom of the mast. (almost one mm space difference causing even more play in the mast). And he says he does not understand the choice of materials.
"Why the chewing gum aluminium instead of a decent suitable alloy?" were his words.
He offers to take the entire mast and slide plate of and use only the body of the faceting head.
He used a lineair rail for the mast and also for the slide plate. He put some decent preasure bearings in the mast so can rotate. He fixed the fine height adjustment with a micrometer.
The dial indicator also had a lot of play and was not repeatable so I put a different (more accurate) dial indicator on the machine. Now it is repeatable and very accurate.
I am very happy with the adaptations and the results! And I have finally been cutting a few stones since I picked it up.  beers

I wrote Zane another email with some pictures from the adaptations, and the things that the machinist had said about the machine, and a list of all the problems that I had encountered with it. He replied saying that he felt I was insulting the machine, and said he did not really feel like compensating me while I was "insulting" the machine.
I told him to just send me the correct controller for the motor, and to leave the compensation if he did not feel good about it.
That was a month ago and I have not heard from him since..... no email, no controller......nothing.

I find it absolutely incredible how much problems I have had with this machine! And I truly dont understand how this machine has such good reviews on forums. I have been emailing polymetric for over three months but none of the problems were solved and I still dont have a new motor controller.

Here a few pictures of the machine after the adaptations. I will do a separate post soon about all the adaptations that have been made to it, and probably will be done in the future. (I want to put different encoder on it, etc. etc.)

« Last Edit: June 11, 2020, 06:35:10 PM by Giel »


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Re: My new faceting machine (a horror story)
« Reply #1 on: June 11, 2020, 07:24:20 PM »
Has your machine an encoder on it ? If it does you could put a higher cpr encoder on it and use a another display. Have you Tom Herbst books ? Pretty sure he has/had a polymetric he fitted an encoder to.
If you are interested in doing the encoder, show me some pictures of it and I'll let you know what I think and which to buy to replace it.MB


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Re: My new faceting machine (a horror story)
« Reply #2 on: June 11, 2020, 09:52:23 PM »
My machine has a potmeter.
I ordered Tom Herbst books along with yours.  ;D
I went straight to the chapter about fitting an encoder.
I already searched online for an encoder, and found a few potential candidates at US digital.
Before I order one, I will definately contact you for some advice.


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Re: My new faceting machine (a horror story)
« Reply #3 on: June 12, 2020, 09:06:29 AM »
Definitely do not order anything before chatting with me :)
You are going to need a 5000cpr 20000ppr encoder. US Digital is very expensive. Large electronics wholesalers like digikey and arrow are potentially cheaper for the encoder.
Your Netherlands? Free shipping over 50euro I think. If you can adapt to have a 6mm shaft on your machine to connect to they have stock.5000ppr in the description in incorrect it is cpr in the datasheet.

AEDM-5810-Z12 48.76euro. add some capacitors/resistors/other bits and you'll be over 50euro. Then it doesn't hurt as much if you blow it up compared to US Digital.

I am using same but Z06, Z is 5000cpr, 06 is 1/4" shaft. 12 is 6mm shaft.


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Re: My new faceting machine (a horror story)
« Reply #4 on: June 19, 2020, 02:45:47 PM »
I was thinking about using a 10000 cpr encoder. I would rather pay a bit more and have a very precise digital readout.
I had been looking at this one:
Or even this one at 60000 cpr (allthough that might be overkill)
So far I did not really learn much about the rest of the setup; arduino. software and electronics.

I have been cutting a few stones and I am running into even more problems with the machine. so I have to get that fixed first!
The dop sticks in the machine dont run true and also have a "runout", giving me a slightly oval stone instead of a round one.... :(
I measured different dop sticks in the faceting head and marked the high and low positions, on the machine and on the dop.
I put the dops in the machine at different positions. (turned them a bit every time)
That way I know the runout is in the machine, not the dops.


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Re: My new faceting machine (a horror story)
« Reply #5 on: June 19, 2020, 09:04:07 PM »
It might not be all the dops, I remember Tom Herbst saying he was frustrated with rotational error on his machine. A huge amount of dops are a bit bent on most machines, you can lap them in a bit to make them better.
Given you are getting your machine really true you may be able to go a higher resolution encoder, 5000cpr, 20000ppr is a nice balance with my machine. Anymore and the lap flicker is going to become a problem.You are looking at encoders with a 2inch diameter code wheel, they jump up in size above 5000cpr. Make sure you can mount it easily.

« Last Edit: June 19, 2020, 09:07:13 PM by MakkyBrown »


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Re: My new faceting machine (a horror story)
« Reply #6 on: June 20, 2020, 07:12:04 AM »
I fixed the runout of the collet already. Zero runout now with different dops in different positions!  beers
Used the new brass dops that I bought and measured on the 1/4 inch dop shaft instead of the dopping part itself.
Had to touch the set screws that the manual says not to touch.... ;D
Just finished the pavilion of your butterfly design, will do the crown tomorrow.


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