MB concave build

[Faceting Frank]

I don’t know much about concave cutting attachments, but I do know the quill is going to have to travel in a perfectly vertical trajectory as you alter the angle. If it doesn’t then it will be moving to the left or right of centre as you alter the mast height.
 My mast is the same as Ultratech. But what I had to do to my machine to get the quill 90deg to the lap and allow me to cut the stone in the picture from 90 to 20 deg. Keeping all facets aligned without using the cheater, is to have an adjustment for the quill pivot, altering this by trial and error till I got it right.

[FlashGP]

Hi Frank,

Pretty much the same issue, but the cylindrical cutter on a concave cuter adds two more dimensions of error. 

With a flat lap on an ordinary faceting machine, the plane through which the quill pivots must be perpendicular to the top of the lap and the plane through which the stone sweeps across the lap must be parallel to the lap. 

The vertical quill pivot plane on the concave cutter must still be perpendicular to the top of the cutter, but it must also be in the same plane as the centre of the cutter as it travels back and forwards.  If it is parallel to that plane, then the facets will be off-set, that is when at 96, they may be cutting as if set to 2 or 94.  This is because the stone is no longer sitting on top of the cutter, but part way around its circumference.

If the mast is off-set (as in the GemMaster) and this is not compensated with the Quill positioning, the cuts will be tilted on the stone.  It's why you need to be able to adjust the position of the cutter relative to the quill so it is perfectly aligned.

regards
Gordon

[Faceting Frank]

I’ve looked at the whole of this thread now and realise my comments would have already been thought over.
Don’t know if you guys could put a digital Vernier to use. I have one on my mast and use it to keep a record of its position on different rows of facets, or individual facets on some comp. stones. Allows me to get back to any facet with absolute confidence I’m spot on. Bought it at Hare & Forbes part number D667.

[FlashGP]

Hi Frank,

I use a Facetron on which the mast pivots.  The mast passes through the aluminium block that is the body of the faceting head.  As a result it would require a fair amount of engineering to mount a digital vernier. 

But because my protractor is permanently calibrated and runs off a crank and odometer, I have added a 1/100th degree scale besimide the tenth wheel.  This plus the dial indicator allows me to come back to the same height after changing angles.

Because I use laps of varying thickness, it is probably easier to use this setup than a digital vernier in the mast.

Regards
Gordon

[FlashGP]

Hi Makky,

About your reallignment issue with the concave cutter on the Gemmaster.

Thinking it through, you may have to add an adjustment to the pivot lock so you can compensate for the offset of the quill.

Regards
Gordon

[MakkyBrown]

I plan to cheat a bit flash if I have too and use the pivot of the concave cutter assembly to help with the alignment. Maybe i could make an adjustable 0 indicator.
I am about to start focusing on book volume two, I have 80 designs to work though, start test cutting and formatting and remove a few with the aim of having 60 really good designs I am happy with for book volume 2.So concave machine will be on hold of a bit until I get on top of the book. :)I am really happy with how most of the new designs render and can't wait to cut them 
I'm thinking it will be better than volume 1.
CheersAndrew

[FlashGP]

No worries, I'm looking forward to seeing volume 2. 

I showed Volume 1 around or local facetors group meeting on Sunday, a number of the members were impressed.

regards
Flash

[Giel]

I have been away from the forum for a while, and my own concave build has been on hold.

I just wanted to say: Awesome build Makky!!! 
Looking very professional, god I wish I had a neighbour like you with a cnc machine and a lathe.

Also thumbs up to Frank for the faceting machine, that's the best homemade machine I have seen on the internet!

[FlashGP]

Hi Giel and Makky,

I hope you are both entering at least the concave cut stone in the Australian Facetors Guild 2020 annual competition.

I didn't enter the concave stone I was cutting as I alligned the concave cuts to the wrong guide facets so the pavillion was2 index stops off allignment.  Mrs Flash scored the stone. 

There was 1 concave section entry in 2019, not bad as it is a new section, but I would like to see more entries in the the 2020 comp as I believe the 2 optional sections (the concave cut and the Open Challenge) add interest and encourage diversity.

I cant enter the 2020 comp as I am one of the organisers.
Regards
Flash

[Giel]

Hi Giel and Makky,

I hope you are both entering at least the concave cut stone in the Australian Facetors Guild 2020 annual competition.

hahaha, that would be fun, but my new faceting machine has yet to arrive, my concave build is going slow as I am not a machinist and have to wait months for parts. Above all, I am spending it all at the moment on the new machine and laps. 
And I consider myself a bit of a beginner, and I'm dutch.

But in time I will enter if possible. 

[Faceting Frank]

Barry Chapman was the only entry in the concave section.

[FlashGP]

Hi Geil,

I know about going slow.  I built my concave cutter from bits from Banggood.  Direct coupling the collet holder to the motor with one Thou shims to centre the collet holder on the shaft has given me more accuracy than a 150mm extension shaft mounter on bearings.

Anyway, you only have 7 more months to complete your machine and submit your entry, plenty of time to finish the concave machine.

Regards
Flash G

[Giel]

I know about going slow.  I built my concave cutter from bits from Banggood.  Direct coupling the collet holder to the motor with one Thou shims to centre the collet holder on the shaft has given me more accuracy than a 150mm extension shaft mounter on bearings.

Maybe I should let go of the idea to make it perfect....
Just build it and get cutting, I will probably modify it later on anyway.
I have a collet holder that fits the motor and I also have an extension shaft with bearings so both options are available.

Anyway, you only have 7 more months to complete your machine and submit your entry, plenty of time to finish the concave machine.

hahaha, amping up the pressure.....

But seriously, if possible I will enter. (never entered a cutting competition before though)

[MakkyBrown]

I'll enter aswell Giel. Just build it is the best approach, as you'll probably find unexpected issues you will need to change.
CheersMB

[Giel]

I'll enter aswell Giel. Just build it is the best approach, as you'll probably find unexpected issues you will need to change.

Yeah I know that I will probably run into unexpected issues, I already am while building it: I need to find a metal worker in the area for some parts, need to find a nerd to help me with the dc motor and driver, because stepper online will not answer my emails.
slowly but surely I am getting there.