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#226

Dihusky
Member
From: Gold Coast, QLD
Joined: 16 June 2017
Posts: 190
Member
09 May 2018 08:42 am

SneakyCuttlefish wrote:

Sorry guys might have to take a rain check on this project. I am having a few accuracy issues with the facetron head. I'll have to send it away for a tune up. Something wrong with the dop locking mechanism. I'm assuming its worn or just got some grit in it that won't let the dop lock in perfect alignment. Anyway, its a good oportunity to have it serviced and checked over professionally.

Also a good chance to stock up on new laps and diffrent polishing compounds. big_smile

I've waitied 10 months to do this project. I guess I can wait a bit longer.

Yes you mentioned you were having trouble with your alignment. I have this little jig which overcomes all alignment problems, ok my machine doesn't have any alignment system either so all alignment is facet based, but this little system is 99.9% accurate.

1525815392_dop-alignment-jig.jpg

Works by setting the quill level at 90 degrees and zero on the index, touch down into the clamp with the bottom feet on the master lap, tighten the clamp then remove the dop. Place a clamp on the transfer dop, transfer then install the dop into the quill with the clamp feet on the master, tighten the quill. Job done and everything should align perfectly.

1525815406_dop-clamp.jpg

The little dop clamp.

1 user likes this post: 7.62marksman

#227

SneakyCuttlefish
Member
Joined: 24 June 2014
Posts: 264
Member
09 May 2018 03:21 pm

Looks like a neat tool dihusky!! Wish i had one like that for my old graves.

Facetron have keyed dops. They use a very similar system to your jig except the keyed part of the dop sits in a groove and is locked down. Ive tested the transfer jig and its spot on.

Most of the time any accuracy issue i encounter is a problem of my own making. I use wax for dopping and on occasion i have heated the stone too much and softened the bonded wax. Wax dopping is more an art than anything else and I dont always get it right. One time i encountered a slightly bent dop. Hard to diagnose. Nearly did my head in trying to figure that one out!!! roll

However, the recent string of complications arise when reinserting the dop into the quill. I can cut a perfect facet, release the dop then reinsert it and the facet is off.

From my understanding the locking mechanism in the quill is similar to a cam. It presses the flat part of the dop to lock it in. Im assuming the angle of the cam is slightly worn which is creating the issue. Most likley from some diamond dust that got in there.

I have asked to have the entire quill replaced and this time round ill be using a small rubber grommit around the dop to keep the water and grit out.

#228

Dihusky
Member
From: Gold Coast, QLD
Joined: 16 June 2017
Posts: 190
Member
09 May 2018 03:44 pm

Yep SC, the Graves is what it was originally designed for, now my mate makes them in small batches for 6.5mm dops so they can be used for any machine.

How on earth did you manage to bend a 6.5mm brass dop?? Buy a set of feelers and roll your dops on the master and see if a feeler passes between any of the dop shafts and the master, if it does they're bent and get the 'heave ho'. A bent dop will send your mind to hell and back!! mad mad

#229

SneakyCuttlefish
Member
Joined: 24 June 2014
Posts: 264
Member
09 May 2018 05:41 pm

Thats for sure. The bent dop was from a huge mistake i made on my second attempt with a BAST lap. Never used a soft metal lap at that time so when I introduced a facet to aggressively and one tooth out of alignment (it was 10pm and I was tired), she bit in hard enough to shatter the stone and take a huge gouge out of the lap. Sent the machine away to be professionally callibrated and tested after that and it came back 20/20 but never thought to check the dop. Wasn't until months later (and many stones later) I used that particul dop again and spent three days in screaming madness trying to work out what was wrong.

Now days I turn the machine off and double check the postions for facets changes on the final polish. Adds an extra 15 mins to cutting time for bigger stones but its absolutley worth it to get the final polish 100% (and not destroy a ridiculiously expensive polishing lap)

#230

Lefty
Member
Joined: 01 May 2014
Posts: 1,300
Member
09 May 2018 06:04 pm

Most of the time any accuracy issue i encounter is a problem of my own making. I use wax for dopping and on occasion i have heated the stone too much and softened the bonded wax.

This can be a problem with sapphire, especially if you polish on a ceramic lap which doesn't act as a heat sink near as well as a metal lap. Because I usually polish sapphire on ceramic, I usually dop them with epoxy from the start - had too many heat up, soften the wax and turn out of alignment back in the early days.

I still dop lots of other stones with wax, the advantage is that it reaches maximum strength in about a minute or two.

A bent dop will send your mind to hell and back!! mad mad

I heard that!!!!

Only had it happen to me once, a small dop that I guess I pushed to hard on. Took me quite a while to work out what the problem was - I reckon I aged about 10 years in a few weeks big_smile

#231

SneakyCuttlefish
Member
Joined: 24 June 2014
Posts: 264
Member
10 May 2018 08:05 pm

Thought I might put up a "hot tip" post for identifing alignment issues having to do with jigs, dops and machine.

Easiest way is to get your hands on one of these below. Facetron supply them with their machines however I'm sure any good machinist could lathe one up for your needs. This is called a target dop. The center point is the truest centre point and is made specifically to suit each transfer jig. Its really simple to use and has multiple functions.

1525935883_20180510_162316_480x640.jpg

Use 1. Checking transfer jig accuracy

Place the dop in the base of the jig and a 3mm dop in the top and lower it onto the target. If the 3mm dop is off its either bent or the jig is stuffed. One thing to watch out for is keyed dops. Facetron keyed dops have to go into the jig with the same orientation on both sides otherwise it will be way out.

1525936013_20180510_165007_640x480.jpg

Use 2. Checking a bent dop

There are 2 kinds of stair-stepping girdles. Before transfer and after transfer. If you are dealing with stair stepping girdles BEFORE transfer you can bet your ass something is very wrong. It is sometimes possible that an issue like a bent or worn mast, misaligned platen or rubbish laps can cause the problem but if your machine is well looked after and maintained, these kinds of problems can be ruled out almost immediatley.

Diagnosing a bent dop will require identifying 2 symptoms. First symptom, as described, is stairstepping girdles before transfer. Even if it is only very slight. Second, you will need to cut your stone to a point as accurately as you can either using the dial indicator/digital indicators or to sound. Then you will need to put the stone into the jig and test with the target dop. If its off centre you most likely have a bent dop.

Image below is about as far as I got with the smoky before I realised something was wrong. As you can see the transfer jig and dop a perfectly ok. The next step from here is to start working my way back up the machine to diagnose what issue could possibly be causing the stair stepping girdles. I have sent the head back to the States to be professionally calibrated and have the quill replaced. I will also be picking up a new mast just to be sure everything is spot on. Probably overkill but I don't want to be down for any longer than I have to be.

1525937544_20180510_162641_640x480.jpg

Notes on stair stepping girdles:

As discussed above, stair stepping Before transfer is a huge red flag. This means something is wrong with the equipment or the bond (wax, glue etc) is shifting as you are cutting.

Stair stepping AFTER transfer is a whole diffrent kettle of fish. There are two very common causes to this frustrating issue. Either it was a bad transfer, or you forgot to zero the cheater before you began cutting the stone. Bad transfers can be difficult to correct if the stone has shifted along multiple axies. i.e bad transfer caused stone to rotate to the left and dipped slightly forward. Nightmare to correct mad mad

Forgetting to zero the cheater is not a big issue. Just adjust where nessecary and test. I like to leave a bit of meat on the crown as I cut the first sequences in. That way I can check for stair stepping before setting the girdle thickness. It pays to be extra careful when cutting high value material especially when dopping with wax.

Best way to zero the cheater is as follows (works best for keyed dops):

  • Make one of these below. Its a piece of thin glass approx.. 1 inch long, dopped perfectly between 2 dops.

  • Grind it to a flat edge.

  • Colour the flat edge with a permanent marker

  • Switch the tool over to the opposite side and LIGHTLY touch it to the lap at 90 degrees

  • If the marker is ground off one side but not the other the cheater is out and you need to adjust accordingly. The aim is to have the entire length of the glass touching the lap instantly.

1525942591_tool_640x424.jpg
1525942620_machine_640x480.jpg

The longer the glass edge the finer the zeroing. However, the longer the edge the more difficult and time consuming it is to zero. 1 inch works a treat for me. A perfectly zeroed cheater should look like this:

1525942637_zero_480x640.jpg

If you do encounter a difficult problem then the best way to solve it is almost always take a break, have a coffee and come back to it. Its amazing how many variables ones subconscious can crunch in the back ground.

2 users like this post: Billy, 7.62marksman

#232

Mackka
Member
From: Brisbane
Joined: 18 February 2014
Posts: 2,429
Member
10 May 2018 08:52 pm

I don't understand any of It Sneaky, but by the livin gingo your photos and explanations are very well put.
I absolutely love the photos, thank you.
Mackka

1 user likes this post: roddosnow

#233

SneakyCuttlefish
Member
Joined: 24 June 2014
Posts: 264
Member
10 May 2018 09:07 pm

Cool! thumbsup Glad I could clear that one up for you mackka! lol lol lol lol lol

2 users like this post: Mackka, roddosnow

#234

Dihusky
Member
From: Gold Coast, QLD
Joined: 16 June 2017
Posts: 190
Member
10 May 2018 10:52 pm

Interesting alignment tool and love the trick with the piece of glass SC. thumbsup thumbsup

#235

Lefty
Member
Joined: 01 May 2014
Posts: 1,300
Member
11 May 2018 08:27 am

Neat centring tool there SC thumbsup

Do machines other than the VJ come with a T-dop? It's a keyed dop designed for zeroing the cheater.

#236

SneakyCuttlefish
Member
Joined: 24 June 2014
Posts: 264
Member
11 May 2018 09:32 pm

Not sure what you mean by a t dop lefty. Do you have a pic? Its possible that is something unique to a vj as they are a completely diffrent cutting concept to most other faceting machines.

#237

Lefty
Member
Joined: 01 May 2014
Posts: 1,300
Member
11 May 2018 10:09 pm

I think there might he a pic of one at the VJ site but I can't post the link from this device. I'll take a pic if there's not one there.

Basically, it's similar in concept to the glass between two dops. You set the machine at 45 degrees and insert the keyed t dop which has a flat bottomed bar attached tot he end and use it to determine level in a similar way.


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