Granite Optical Bench Construction

[richard martel]

Bob,
I sucked the water out of the dam with my wifes turkey baster...I'll know tomorrow if any granite dust was found Ha! I'll be keeping the moment arm of the camera and StackShot as close to the column as possible for reasons you said...Thanks

Craig,
Thanks for the link. interesting to see that they are using the fabrication parts available fro AluFab. But my setup will be similar.

Andrew,.
I'll be using both types of lighting. I'm sure it is "overkill" for flash especially with my 5D II. But I don't think I'll be limited when I start playing with High magnification projects.

Chris,
I looked into steel plate. you are correct It is denser than granite about 3x as I recall, but the price is also about 3x the cost, by weight. My granite plate set me back $50. Machinability? True but lots of holes. If one looks at this site sent by Craig, http://www.saphicon.com/motorized-lift.htm you can see all of the holes drilled and tapped into the plate and the cost. On order are two blank aluminum fixture plates 1/2x9x12 & 3/8x6x6 that will be attached to the granite plate and the slide on the column. These can be easily removed, drilled and tapped for almost any configuration that may arise.Even taking into account the differance of coefficient of expansion between the aluminum and granite.

[richard martel]

The holes are finally done,



A quick assembly of the column, feet and inserts to check on fit into holes...Good to go!




I the two pics below are the bolt, nylon washer and insert.
I wanted the insert to be slightly below the level of the granite plate so when the column assembly was bolted to the plate, the brackets would be bearing on the granite and not the insert. To accomplish this I used a nylon washer about 1/16 thick (.063") between the insert and the bottom of the mounting feet. The 5/16-18 HH bolt is not the bolt that will be used for the final assembly, but was chosen for it's length. I wanted a bolt that would reach the bottom of the insert so no epoxy would get up and into the threads of the insert. The bolts that will be used, button hex heads are shorter than the bolts shown and will not 'bottom out' into the epoxy.



In order to provide a path for the excess epoxy to flow, I shimmed all three feet with some banding material about .025" thick. This way the column will sit flat on the plate and the feet will be off the plate by the thicness of the banding. The excess epoxy flowed out just fine.

[Mitch640]

Were you planning on using any bedding compound around the extrusion and brackets?

[richard martel]

I decided to use the slow setting JB Weld because it has a pretty high tensile strength. Then,[ prior to epoxying the brass inserts were washed with acetone to remove any oils and the bolts, nylon washers, bottom of feet and column were given a coat of paste wax to prevent the epoxy from gluing every thing together. The bolts were just snugged up to the inserts, not tight at all. I used the wood stick to coat the inside walls and bottom of the holes and then added enough epoxy into each holes to insure a good bond. I used the brush to coat the insert threads with epoxy. It helps if you have an extra pair off hands to mix up the epoxy. If you mix up too much it will start to kick and you won't be able to get all the holes and inserts done in time..About 20 minutes working times at 75F. Placing the column into position I used a long clamp tp pull it down onto the plate. The epoxy slowly flowed out from the holes and under the feet. After letting the epoxy kick off, about 3 hours at 75F, I removed the bolts and column. Using a razor blade I removed the excess epoxy and then picked out the nylon washers. You can see after removing the nylon washer the insert sits below the top surface of the plate and the grey epoxy.





After cleaning up the wax I loosened the four bolts on each foot and let the foot contact the table. tightening these bolts I the used the button head bolts to finish the job I did not tighten the bolts that go into the inserts as I want the epoxy to cure as long as possible. After a weeks cure one can snug the bolts up.



well...this part is done and I'm pretty happy. if I had to do it over I would put the front foot plate on the rear to load it in tension but I'm sure it is just fine the way it is. The next step is mounting the fixture plates...stay tuned

[richard martel]

These are the Sorbathane isolaters. picked for a 75 pound load.



In use

[Bob^3]

Very professionally done, Richard! I look forward to your next installment.

I feel compelled to comment on how well the warped sense of humor of this group matches my own!

No need to be in a hurry, we'll all get our piece of granite eventually.

Speaking of which, a monument place, and most towns will have one, might be a place to find it at a decent price. You could even get it monogrammed, you know, let it do double duty. Who said you can't take it with you? LOL

I sucked the water out of the dam with my wifes turkey baster...I'll know tomorrow if any granite dust was found Ha!

[Chris S.]

Chris,
I looked into steel plate. you are correct It is denser than granite about 3x as I recall, but the price is also about 3x the cost, by weight. My granite plate set me back $50. Machinability? True but lots of holes. If one looks at this site sent by Craig, http://www.saphicon.com/motorized-lift.htm you can see all of the holes drilled and tapped into the plate and the cost. . . .

Richard, I wasn't referring to a pre-made optical breadboard such as that--just a slab of steel with only the necessary holes drilled and tapped. My steel came from my fabricator's scrap box, and iirc, I paid 10 or 11 cents per pound, so comparable with your granite. And though I didn't drill or tap the holes--Don Wilson, my fabricator, did--it seemed my easier than boring granite and epoxying in a threaded insert. But there are lots of ways to skin a cat, and yours should work very nicely. I also suspect someone might do a nice job with concrete, bedding threaded components before it sets up.

As for the "ringing like a bell" posts, I don't think this is important in practice. My metal rig certainly doesn't ring. The purpose of the base plate in a rig like Richard's is to provide mass. This mass is isolated from outside vibrations by the Sorbothane. How about vibrations produced internally to the system? Few if any would be traveling across the baseplate. These would likely be coming from somewhere on the metal mast itself (such as camera mirror/shutter or stepping motor). Avoiding or dampening those internal vibrations is a different matter--though no doubt one that Richard has thought out well.

I could only see the vibrational conductivity of the baseplate material being important in a situation where vibration is being produced on the baseplate itself--which is an unlikely situation. In practice, those who chose stone, metal, or wood baseplates all seem to make the materials work.

[AndrewC]

Looking good

Had you thought of perhaps just drilling 4 through holes through the granite, tapping the convenient 4 holes in your upright and bolting it straight on ? I've done that a couple of times, but never tried to lift a gravestone with it ! In the same vein, why not use your current brackets and drill straight through the granite and through bolt it ? Or why not use expansion bolts rather than inserts ? I love messing with epoxy but I'm never sure how strong it will be.

[rjlittlefield]

How about vibrations produced internally to the system? Few if any would be traveling across the baseplate.

It was an odd case, but I actually have had enough shutter shock couple through to a specimen stage to ruin an image. The oddness involved a heavy subject on a thin pin. Apparently the shock was setting the specimen to oscillating. Beanbagging the camera & lens didn't help, but one around the subject stage worked wonders. That was using my usual wood framework, with the camera mounted on a 35 pound screw table.

--Rik

[richard martel]

Regarding epoxied inserts into granite.
The following is taken from Starret's FAQ"s on surface plates

" 22) Isn't there a danger of pulling epoxied inserts out of the plate?
A) Inserts that are properly bonded using high strength epoxy
and good workmanship will withstand a great deal of torsional
and shear force. In a recent test, using 3/8"-16 threaded
inserts, an independent testing laboratory measured the
force required to pull a epoxy-bonded insert from a surface
plate. Ten plates were tested. Out of these ten, in nine cases,
the granite fractured first. The average load at the point of
failure was 10,020 lbs for gray granite and 12,310 lbs for
black. In the single case where an insert pulled free of the
plate, the load at the point of failure was 12,990 lbs! If a
work piece forms a bridge across the insert and extreme
torque is applied, it is possible to generate enough force
to fracture the granite. Partially for this reason, the Federal
Specification gives guidelines for the maximum safe torque
that can be applied the epoxy bonded inserts.

--------------------------------------------------------------------------------

Thread Size Torque Rating

--------------------------------------------------------------------------------

.250 7 ft. lbs.

--------------------------------------------------------------------------------

.3125 15 ft. lbs.

--------------------------------------------------------------------------------

.375 20 ft. lbs.

--------------------------------------------------------------------------------

.500 25 ft. lbs.

--------------------------------------------------------------------------------

.625 30 ft. lbs.

--------------------------------------------------------------------------------


These figures are extremely conservative and were based partially on the fact that several surface plate manufacturers use helicoil inserts or inferior grades of epoxy."

Andrew,
I'm sure the ways you suggested would work as well...If these inserts pull out I can drill through the block and try again.

Chris,
I really like your rig. In fact It was one of a few that inspired me to attempt a build the one you see here. Yours has the convenience of portability too ???
The azimuth, x,y and goniometer adjustment are sure nice and I'll most likely plagerize your idea. I want to be able to illuminate the subject from below also. This may mean two different hardware arrangements for subjects. I have a lot of reading & learning ahead.

Thanks all for the kind words and suggestions.
Regards, Richard

[AndrewC]

...l..If these inserts pull out I can drill through the block and try again....

..

I'm sure they won't One suggestion, though you probably already have this on your list, I'd take the time (while you were waiting for your epoxy to fully cure) to insert a few parallel rows of smaller inserts for bolting down other parts.

[richard martel]

Hi Andrew,

I do have to put in four more inserts. I have an aluminum plate on order that is 1/2x 9x12. This plate will be drilled and tapped for whatever I decide to mount on it. Commonly called a fixture plate. It is very flat and stress relieved, it machines nice as well. This will be bolted to the granite plate using the additional four inserts for mounting points. It will be easely removable to perform any work on it.

thanks again, Richard

[PauloM]

Richard,

I am following you project with great interest, and I appreciate you sharing your pictures and techniques with everyone here.

Regarding that aluminum plate you mentioned, that you intend to tap and drill (to make a breadboard-like base, I assume), have you thought about using a magnetic base instead? I have a Newport M200 and you wouldn't believe it's gripping power on a steel surface. It would, of course, be movable to whichever position you would like, and so it would save you from having fixed holes in place that someday you may wish they were somewhere else.

Cheers,
P

[elf]

Hi Andrew,

I do have to put in four more inserts. I have an aluminum plate on order that is 1/2x 9x12. This plate will be drilled and tapped for whatever I decide to mount on it. Commonly called a fixture plate. It is very flat and stress relieved, it machines nice as well. This will be bolted to the granite plate using the additional four inserts for mounting points. It will be easely removable to perform any work on it.

thanks again, Richard

I'd recommend using steel for the fixture plate to allow using magnetic holders, but since you already have it ordered, perhaps a relatively thin sheet of steel could be epoxied to the top of the aluminum plate.

I think you could also easily convert this to a horizontal setup by simply bolting the aluminun extrusion flat instead of standing up.

All in all, it looks like it's going to be a very nice setup.

[richard martel]

Thanks for the idea of using a steel plate and magnetic base. Right now I'm lurking on ebay looking for "stuff" to use. The plan is to build the unit so it will cover the most photo possibilities. Some of the Newport tools look good...I may have to go back to work though.

Regards Richard