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Author Topic: Resurfacing polishing laps  (Read 676 times)

Giel

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Resurfacing polishing laps
« on: April 05, 2020, 03:41:50 PM »
It has been a while since I posted on the forum.
I ordered a new faceting machine in the beginning of october, and I also ordered 3 polish laps from gearloose.
The laps arrived, but the machine took a while longer so the laps had to wait.
When the machine finally arrived and when I finally solved all the issues with it, (well not all, I will spare you the horrific details for now) I cut my first stone on it.
When I put on a darkside polish lap, the lap was just tapping my stone! It was not flat!
So I measured the height across the lap, darkside lap had a max height difference of 0,22 mm.
Just to be sure I measured the other two laps, the batt lap has 0,15 mm max height difference and the diamatrix 0,11 mm.

Contacted gearloose and that was way over their tollerance, I got offered a refund which I accepted, expect their email after the weekend.
Jon said that that maybe I had a bad batch, or maybe it was from shipping, as I live in europe.
He cannot send me other ones at the moment as it is Covid mayhem so shipping is not possible right now.

I found someone with a lathe in the area and want him to resurface the laps.
Can he resurface them with a regular lathe bit or does he need a special diamond cutting bit?
The laps are new so there is no diamond in or on them.
i read that normally you resurface with a diamond bit, because of the diamond embedded in the lap, is that diamond bit also to get the right surface finish on the lap?
Can you get the desired surface finnish for the laps by just resurfacing them in a lathe with a regular cutting bit?











Rusted

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Re: Resurfacing polishing laps
« Reply #1 on: April 05, 2020, 04:57:57 PM »
Hi Giel

I think you should be good to go with a good tungsten lathe bit, I resurface my own polishing laps from time to time with just a tungsten tipped tool and it is fine. It can be hard on the tool with the first cut because the diamond quickly takes the edge off but a new sharp tip and the surface will be perfect.
I resharpen tungsten tools using an old diamond faceting lap, no good for faceting but plenty of life for sharpening tools.

Prooz

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Re: Resurfacing polishing laps
« Reply #2 on: April 05, 2020, 06:45:28 PM »
It seems strange to me that 3 new laps would have that much run out! It's not the machine is it? Just my thoughts.

Cheers

Faceting Frank

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Re: Resurfacing polishing laps
« Reply #3 on: April 05, 2020, 07:02:47 PM »
I'm thinking machine as well, never had anything close to those tolerances out.

geowork

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Re: Resurfacing polishing laps
« Reply #4 on: April 05, 2020, 07:12:07 PM »
Hello Giel,
First thing you need to do with a "new" faceting machine is check it out and adjust if necessary. For example and in your case, first check the sweep of a blank dop across the master lap. How does the master look? If not too good, then the sweep needs to be adjusted. If the master appears "flat" and the sweep is uniform across the master, then test the laps. All the best.

Giel

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Re: Resurfacing polishing laps
« Reply #5 on: April 05, 2020, 08:22:52 PM »
Quote
First thing you need to do with a "new" faceting machine is check it out and adjust if necessary

I know and I did.

Quote
I'm thinking machine as well, never had anything close to those tolerances out.

I understand that would be the first impression.

I Calibrated the machine following this method;
http://lapidaryworld.com/pdf/faceting_machine_alignment.pdf

I have a scintillator 88 so I followed the instructions exactly like in the pdf.
Attached digital callipers to the table dop and put that in the machine, rubber band, marked the platen and the lap etc etc.
To my big surprise the flattest lap I found was a nubond 1200, max 0,02 mm (but closer to 0,01 mm) height difference across the lap.
I calibrated platen with this lap, spend an afternoon to get it perfect.
When I rotate the lap now 180 degree on the platen and measure the lap again the readings are the same across the lap as in 0 degree position.

This morning I took measurements again, as the lathe guy asked me to so to identify the problem.
I did the following for each lap:
Measured the lap at 12 positions around the lap 3 times (7,5 inch from center)
Took the lap of and put back in 0 position with the platen, measure again 3 times 12 positions
Rotate to 180 position, measure 3 times 12 positions
Take the lap of and put it back on again in 180 degree position measure 3 times 12 positions
At last I did a 90 degree rotation on the platen and measured 3 times 12 positions

There is maybe 0,01 to max 0,02 fluctuations in my measurements, because of the way I lower the callipers.
The darkside max height difference; 0,24 mm
the batt lap max height difference; 0,14 mm
the diamatrix max height difference; 0,10mm

I asked Jon from gearloose if this is normal or if the laps need the "settle" while polishing or whatever.
He said max height difference for them should be less then 0,05mm
He said the switched from supplier last year for their backing plates, so maybe I have old ones.
He also said that transport could have caused the lap to bend, even if the packaging looked undamaged.

My stone is running smooth on the nubond my stone is bumping around and getting hit and smacked on the darkside.









Giel

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Re: Resurfacing polishing laps
« Reply #6 on: April 05, 2020, 08:31:48 PM »
Quote
I think you should be good to go with a good tungsten lathe bit, I resurface my own polishing laps from time to time with just a tungsten tipped tool and it is fine.

So if the laps are unused and I did not apply any diamond yet. (only a bit of oxide on the darkside)
It should be fine with a normal bit? or tungsten bit?

The guy with the lathe said he is not sure  if he can reproduce the exact surface finish on the lap as it is now.
Is that really important for polishing later on?
He said you will always see some grooves on the lap from the lathe.
If he uses his diamond cutting bit there will be less grooves and better finish, but won't diamond come loose from the lathe bit and contaminate the lap? (this was my major concern)



Rusted

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Re: Resurfacing polishing laps
« Reply #7 on: April 06, 2020, 11:23:11 AM »
I get a very good finish on my laps using a tungsten tool.
The finish on the lap from the lathe tool is ideal, you have probably heard about people scoring laps to trap the grit for polishing, consider this a much finer and more accurate scoring if you like.

Dihusky

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Re: Resurfacing polishing laps
« Reply #8 on: April 06, 2020, 05:36:32 PM »
The surface finish coming off the lathe will depend on the shape of the tungsten tip and the speed of cross travel. Tungsten finishing tips can have a small radius on the cutting point which with a slow cross travel will produce a very fine, smooth finish.

The most accurate finish will come from setting the back of the lap in a set of machined soft chuck jaws, you're placing the lap against a jaw surface that has been trued to the cross travel of the lathe, and has sufficient depth to just grip the lap without protruding past the lap surface.

Giel

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Re: Resurfacing polishing laps
« Reply #9 on: April 06, 2020, 09:07:50 PM »
Quote
The surface finish coming off the lathe will depend on the shape of the tungsten tip and the speed of cross travel. Tungsten finishing tips can have a small radius on the cutting point which with a slow cross travel will produce a very fine, smooth finish.

The most accurate finish will come from setting the back of the lap in a set of machined soft chuck jaws, you're placing the lap against a jaw surface that has been trued to the cross travel of the lathe, and has sufficient depth to just grip the lap without protruding past the lap surface.

The guy with the lathe was already talking about a tool with a a small radius instead of a point, to get a better surface finish.

He was planning to machine a backing plate to set the lap in the lathe so it is resting on the backing plate all across the back of the lap,maybe even machine a little 1/2 inch arbour to secure the lap, then machine it.
That sounds a lot like what you describe Dihusky.
I will show him the answers from you guys about the tungsten tools and some lap machining info I found on another forum, I guess it will work out fine.

Thanx everybody for the replies and suggestions!
Will let you know if it all worked out.

Rusted

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Re: Resurfacing polishing laps
« Reply #10 on: April 07, 2020, 07:02:04 AM »
The backing plate with the 1/2 inch arbor is exactly what I use.
It sounds like he will get a good result.

Giel

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Re: Resurfacing polishing laps
« Reply #11 on: April 07, 2020, 04:39:37 PM »
Quote
The backing plate with the 1/2 inch arbor is exactly what I use.
It sounds like he will get a good result.

He says he is a bit unsure about the whole job, because the materials are unknown to him. (never worked with them before)
And he is not sure if he can achieve the desired flatness and surface finish.
I get the feeling he is not really looking forward to it...:'(

I have evealuated my endless list of measurements again, and I am absolutely sure it's the laps, not the machine.
If I mark the lowest and highest spot on every lap and rotate the lap 180 degree or 90 degree on the platen, the low and high spot on the lap is in the same spot on the lap everytime. (height of low and high spot fluctuate maybe 0,02 mm max bepending on the position on the platen)

So I am going to have them resurfaced anyway.
I am going to make some more calls today to find someone who is up for the job!

Dihusky

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Re: Resurfacing polishing laps
« Reply #12 on: April 08, 2020, 04:58:54 PM »
To be honest Giel, if he is an experienced machinist the job should be straight forward, the material shouldn't matter.

Giel

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Re: Resurfacing polishing laps
« Reply #13 on: April 08, 2020, 09:11:44 PM »
I found someone else wirh a lathe who makes his own laps and his own faceting machine!
I was on the phone with him this morning, he has a new diamond bit that he will use, and he also has a new lathe, said it wil be flat withing 0,02 mm or something. He charges 30 euro or something.
I will bring the laps to the post office later today.  8)


Giel

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Re: Resurfacing polishing laps
« Reply #14 on: April 11, 2020, 05:38:25 AM »
This guy turned out to be a great new contact!
He is retired and makes faceting machines for fun and sold over 80 of them so far. He is a facetor himself, he makes his own laps which I will definately try in the future. (apparently some cutters in idar oberstein love his laps.
He has a good lathe and and diamond tools and on top of that he is a very funny guy to talk to.

He already called me today that the laps are flat again and he will put them on the mail tomorrow!
I send in the 3 laps from gearloose and one old tin lap I had.
He charged 40 euro for the resurfacing of 4 laps including shipping.  :o
He said the laps were indeed very bumpy or bend and he measured even more height difference in the laps then I did.

Also compliments to Jon from Gearloose for refunding the laps, awesome customer service!
I spend some of the refund on a greenway and a battstick. (thought that was fair given that I still have the other laps)
Jon even put the greenway in the lathe to make it flat before sending it to me.
Not sure if that was a service, or to make sure I cannot complain about it anymore.  ;)
Important thing for me is that it is solved now and that I can start cutting stones in a few days!






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