Side Views of Cabs Please [Dome Question]

[3rdRockFromTheFun]

Wow - I don't know how but I totally missed the cup thing even though I saw the chuck in the picture... BOB - please elaborate! I want to make one of these - that is so cool!

[lithicbeads]

 You can do the initial stage without  grit as I have many times. Get a core drill the size of about 4/5 the diameter of the finished radius you want and preform by hand a stone as round as you can get , Mount the bit facing up and put the preform on it  and start it rotating . You need a piece of copper tubing the same general diameter as the drill core and you hold it to the preform above center off to the side . The preform will begin turning and you move the copper tube to keep a random rotation of the rough until it is round. You then have a marble.
  If you use a dopped stone you rotate the drill bit and move the dopped stone in various motions to grind the half sphere. If you use copper tubes and grit instead of the core drill bit put a bit of rag inside to keep the grit near the top of the tube , The tube edges then become razor sharp so be careful. I modified my all-u -need when I did this and it worked perfectly .

[tntmom]

Carol,

I tried to do a video for you regarding how I preform before doming on a flat lap.  Just like every video though that I have ever attempted, I always have at least one kid come into the shop while videoing and exclaiming "Mom!!!".  

This video is after the roughing out preform and what I do with the girdle and shape before I start to dome it.  I'm certain that I am much different than most as I learned through trial and error regarding what worked best for me.  This is how I start each cab though!

http://www.youtube.com/watch?v=oCTA_-j45Jg&feature=youtu.be

[kennyg]

good job Krystee

[Carol M]

Carol,

I tried to do a video for you regarding how I preform before doming on a flat lap.  Just like every video though that I have ever attempted, I always have at least one kid come into the shop while videoing and exclaiming "Mom!!!".  

This video is after the roughing out preform and what I do with the girdle and shape before I start to dome it.  I'm certain that I am much different than most as I learned through trial and error regarding what worked best for me.  This is how I start each cab though!

http://www.youtube.com/watch?v=oCTA_-j45Jg&feature=youtu.be

Hi again Krystee,
You totally underestimate the value of your videos and your teaching!!!!
This is fabulous!!!  
It's changing the way I'm going to work!!!

After the girdle line, you really 'go for it' in the first angle!!!  It looks from the surface of the stone and from the 180 written on your flat lap disc that this angle is done at that grit. 
Thank you, Thank you, Thank you!!!

Any chance for 'the next step' video  [even if you're using different stones??? [grovel, grovel]

I'm asking because the middle of the cab at this point, which is flat, is [relatively speaking], fairly large.

Also once the girdle is set, since the length of the first major angle is fairly long, is your next move to make another marking line and do progressively steeper angles so that you have a 'series of stepped angles' in flat sections, and then blend them to the top???
Or is that it on the flat steps and you go to the colored sanding discs after one steep angle and just blend it, or what?

I guess what I'm basically asking for is if you could do a Part 2 video.....just like the last one....with the machine turned off and a 'pre-done stone'.....but showing how many 'flat steps' you'd normally do, while you're at the 180 grit.

Or , if that one steep angle 'is it', show 'what's next' in shaping so you don't end up with a large flat spot on top.

Krystee.....you're a doll!!!

Re the kids interruptions....no worries......that's life!!!
They don't call you 'tntMOM' for nothin'!!! 

Thank you, again.
Huge E-Hug,

[bobby1]

Here are some photos of the various sizes of cups that I use to make perfectly shaped half -spheres or fully rounded spheres.  made these on a metal lathe using various sizes of round stock. Some have a
smooth stem for gripping in a Jacobs chuck and others have a 1/4-20 threaded rod for the stems that I use in flat lap machines with a threaded hole for mounting the laps. The hole for the cup is made with various drill bits. They leave a cone shape but it rather quickly wears into a dome shape. If I'm  doing a half sphere I dop the stone so I can hold it for the shaping. For spheres I hand hold the stone. When I'm hand holding the stone I wear exam gloves from Costco because the S/C tumbling grit will really stain your hands. I dip the stone in water then into 120 grit tumbling grit and roll it about in the cup. I then proceed down to 220, 400 and sometimes 600 grit. Then I dop it and go to the polishing pad.
Bob

[Carol M]

Now THAT IS SERIOUSLY CLEVER design idea, Bob.

It blows my mind the things people come up with!!!

Where do you get the POSH stones to make the cabs??
Like do you ever find POSH Amethyst??

[3rdRockFromTheFun]

Those are neat Bob, thanks! I'll have to figure something else out based on that - I have no way (that I know of anyway) to lathe cups. I'm wondering if I could find an epoxy that's hard if I could mold something like that? That idea popped into my head when I was thinking of the pitch laps used for grinding lenses

Krystee - nice! I love your videos - hope you do more! You're especially good at getting to the point and not yammering on about everything else in the world like some how-to vids do (geez those are annoying!).

FWIW Carol, when I was doing girdles I used to make girdle lines by stacking up a few aluminum templates (anything flat hard and thin you can stack will do) then placing my aluminum or brass scribe atop the stack and holding it firm, then I would gently run my preform in circles next to it so that the scribe would make a line on them. Perfect lines every time.

[Carol M]

Those are neat Bob, thanks! I'll have to figure something else out based on that - I have no way (that I know of anyway) to lathe cups. I'm wondering if I could find an epoxy that's hard if I could mold something like that? That idea popped into my head when I was thinking of the pitch laps used for grinding lenses

Krystee - nice! I love your videos - hope you do more! You're especially good at getting to the point and not yammering on about everything else in the world like some how-to vids do (geez those are annoying!).

FWIW Carol, when I was doing girdles I used to make girdle lines by stacking up a few aluminum templates (anything flat hard and thin you can stack will do) then placing my aluminum or brass scribe atop the stack and holding it firm, then I would gently run my preform in circles next to it so that the scribe would make a line on them. Perfect lines every time.

Re Bob's lathed cups - I wonder if they're available for sale on the web??
Re Krystee's Videos - TOTALLY AGREE!!!  Straightforward!!!

Re the Girdle Line, I've just used a thin black magic marker and found that the chubby body of the marker was the right size to just lay on the tabletop and move the shaped preform up to it to mark the girdle height.  That part seemed to work OK for me.
When I was taught, my guru did 'multiple angled sections' however, but the first one was no where near a steep as Krystees.  He went up a bit with progressively steep angles.  Each progressive step had a new marker line for the edge of that step. [tedious as hell though] 

That's why I'm wondering how to get rid of the large flat top.  How many angled steps are there before you get to the 'blending of angles' sanding stages??

[tntmom]

Bob,

Your little cups remind me of the little cups they sell as an accessory attachment for the Graves Cab Mate for small shperes/marbles.   I've never seen them in person but always thought that they would be a cool thing to try.  It never occurred to me to use them to make perfectly domed rounds!!!  Have you seen those before?  Do you think they would be similar to what you have made?

Carol,

As far as what I do next depends on whether I am doing high domes or low domes.  For high domes....  I start at the upper mark at the top portion of the cab where the angle meets the flat spot.  I slowly turn the cab in circles staying on the line, working my way towards the very center of the stone until the flat spot is virtually eliminated, I do this slowly and once I get one complete circle turned then just slightly change the angle a bit more to keep making the flat spot smaller smaller until I get to the center.  Then I color the cab and move on to the sanding disks using my circular technique to smooth out and sand the cab.  For low domes, I will stay on the 180 and start my circular technique right from where I left off in the video.  I will start at the highest angle and as I am doing constant little circles I will slowly keep rotating the cab in a circle as well and make my way to the center of the cab until the flat spot is virtually eliminated.  Then I will color the cab and move on to the sanding disks.  Most of my time cabbing is spent doing the initial shape on the 180.  All the rest of the steps are just sanding and blending it all together.

Lately I have been playing with my expando and diamond belts.  I've found that the technique I use on wheels is completely different than how I cab on a flat lap once I get the initial shape formed out.  On the wheels I do not use any type of circle technique, instead I use an up and down motion with my wrists as I slowly turn the cab in a circle.  I've even been going back and forth between the machines lately as I am finding some things are faster and more precision on the lap whereas sanding is much faster on the wheels.   Everything I do is constantly evolving as I continually learn new techniques!!!

[Carol M]

 I slowly turn the cab in circles staying on the line, working my way towards the very center of the stone until the flat spot is virtually eliminated, I do this slowly and once I get one complete circle turned then just slightly change the angle a bit more to keep making the flat spot smaller smaller until I get to the center. 

Then I color the cab and move on to the sanding disks using my circular technique to smooth out and sand the cab.  For low domes, I will stay on the 180 and start my circular technique right from where I left off in the video.  I will start at the highest angle and as I am doing constant little circles I will slowly keep rotating the cab in a circle as well and make my way to the center of the cab until the flat spot is virtually eliminated.  Then I will color the cab and move on to the sanding disks.  Most of my time cabbing is spent doing the initial shape on the 180.  All the rest of the steps are just sanding and blending it all together.

Hi Krystee,

I'm not usually this 'slow on the uptake' but .......ya lost me in the 'land of circles'..[smile]
I've seen your 'circle technique video' which is used once the shape is basically formed and used with the colored sanding discs.  That part is clear to me.

I really love the high domes but can't seem to get the shaping technique into my brain. 
When you say " I slowly turn the cab in circles staying on the line"......Are these 'in circles' you refer to, following the line in a long circle around the cab, or staying in one spot tiny circles, like your circle technique??  When you do the 'circles' do you keep the cab oriented in one direction and just 'massage the circle' or do you rotate the cab around in a single spot like with the circle technique.  [DUH!!!] 

Any chance for a 'quickie video' just to continue where the earlier one ended with the shaping after the first strong angle?????   

[tntmom]

Staying on the line in the same direction.... something like this:

[tntmom]

I will see if there is some way to video it.  I will be out in the shop cabbing later this afternoon.  I will have to find something I can dop though so that I can do it one handed while video taping.

[Carol M]

I will see if there is some way to video it.  I will be out in the shop cabbing later this afternoon.

Great....take your camera or cellphone [giggle]

That diagram is exactly how I feel [more giggles]

[kennyg]

Krystee I have just recently tried to duplicate your circular technique on a sic wheel 1 1/2 inch wide and have had some good results, It's kind of like patting your head and rubbing your stomach if you have used the traditional style of up and down, back and forth while rotating the stone. It gets kinda comical sometimes trying to stay on track a 3" diamond wheel would definitely make it easyier