Close tolerance drilling of quartz with diamond core drills. 1

[legrand01]

Hello all,

The company I work for is having some issues with drilling through a couple of types of materials we deal with. One is Quartz and the other is a fused silica that is made in house.

The parts that need to be made look very much like thick washers. An sample part might have an OD of .4175"+/-.002 with a through hole of .096"+/-.002 and a thickness of .08". Concentricity of ID to OD is .003"

Currently we are stacking two plates together (along with scrap plates on the top and bottom to minimize edge chipping) and using a VMC with diamond core drills to cut the ID and then the OD, thereby making a "complete part" (tumbling and edge chamfering come later, but they are not the issue).

We also sometimes only drill the ID's then cut squares out and put them on a mandrel and grind the OD down in order to maintain concentricity.

The real problem is that we cannot find a vendor for the drills that will make good quality high toleranced diamond core drills. There are two companies we have been dealing with for quite some time. One makes good quality drills, but not in the size we need. The other will make the size we need, but the drills could be +.005", +.008" or more out of spec.

Does anyone out there have any recommendable diamond core drill manufacturers, or possibly a different method of manufacturing these "washers"? Any assistance would be greatly appreciated.

 

[unclesyd]

I would definitely give Sonic-Mill a call.

We used this method to make multiple holes in different ceramics.

http://www.sonicmill.com/index.html

 

[unclesyd]

One of them brain things came along just as I was posting the previous post. I almost left out Bullen Tech.

http://www.bullentech.com/animation

 

[btrueblood]

What syd said. Also look into abrasive water-jet cutting, but I don't think they can hold the tolerances you need (typical jet-cut holes will have a taper).

From long ago, a technique for drilling holes in glass was to use soft copper or brass tubing chucked in the drill, with the end dipping into a puddle of abrasive compound on the part. Pretty much what your core drills are, but without embedded abrasives.

Can you send the oversize core drills out to a shop that does centerless grinding, and have them re-size the o.d.'s?

 

[btrueblood]

Ok, just two more comments/random thoughts.

The reason for a "core drill" is to pass coolant thru the center, not because you want the core to come away as a solid piece (e.g. for sample), correct? Machinists and machine shops may call a drill with a hollow core by the name "gun drill" instead of "core drill". Dunno.

And, I assume you googled for "micro core drill", and can do the same for "micro gun drill" and "micro hollow drill".

 

[Compositepro]

For those tight tolerances I would think that grinding or lapping would be required after core drilling. Or single point diamond turning.

 

[legrand01]

Thanks for the input. So far this is what I have done thus far:

Sonic-mill: Will look into it, but there is someone here that toured their plant at one time and was less than impressed with their setup. He said they outsourced everything about the manufacture of their machines.

Bullentech: this abrasive jet machining leaves tapered wall sides, which are not acceptable.

I am looking into water-jet cutting and possibly laser cutting as well. I think I will send out some pieces for sample cuts.

Having come into this project "late", I am looking into what was done in the past and with one manufacturer (UKAM) that was used, the company purchased fine and extrafine grit drills from them, then the machinist said they were drilling too slowly. When I brought this fact up to the machniist, he looked as though he didn't even know they came in different grits. This company manufactures decimal size drills so I will attempt to purchase some from them with a coarser size grit.

As for lapping or grinding, you're essentially grinding when you're using a diamond drill anyway, it just depends on how fine a finish you want. Chipping seems to be the major issue with the drilling.

Thanks for the suggestions thus far.

 

[Compositepro]

Your problem is that removal of the majority of material should be done quickly in a "roughing" operation. Precise finish and tolerances require a slow "finishing" operation. It is usually not possible to accomplish both at the same time. However, that depends on your exact requirements. If you can find a way, great.

 

[powerhound]

Have you made sure to indicate your core drills? I worked at a quartz machining company and we did lots of core drilling. The core drills were not exactly concentric to their mounting bushing. We would actually physically tweak them until the ends ran true. The other option is to drill them out small and then interpolate the holes to size.

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Ceramicguy]

I can recommend two vendors that supply metal bonded diamond drills. Both can supply drills with +-.0005" diameter tolerances. Lammers Microdrill in Kutztown, Pennsylvania or KeenKut in Hayward California. Both vendors can work with you to select the best bond material for the application. At the tolerances you are trying to achieve, the drills must run true and the drilling setup must be rigid to prevent instability. Keeping the drills as short as practical will help. Through drill pressurized coolant is recommended for optimum drill performance.

 

[mrquartz]

I've dealt with many diamond tooling vendors... the following 3 companies make excellent diamond core drills in all the various grit sizes & bonds. The first two would be my pick, but Keen Kut (Frank) makes a good product too.

http://www.accessdiamond.com/

http://www.sierradiamondtool.com/

http://keenkut.com/

Laser cutting the part would be the best way to keep those tight tolerances with min. taper on that thickness. I'm familiar with the Mitsubishi laser.

Core drilling on a VMC can be tricky with those small diameters, and tight tolerances, but can be done. There are two ways to go about it but too lengthy too discuss. There are several things that come into play besides the core drills (mentioned by powerhouse). I wouldn't wax more 5 or 6 parts together, keeping the thickness under 0.500". The shorter the better. The bottom part would be throw away but reduces the blow out. I'm familiar with the Haas VMC.

Water jetting could work, depending on the waterjet, abrasive size & nozzle. You shouldn't have a taper problem cutting that thickness. You could get away with waxing 3 or 4 together... the bottom part would be throw away but reduces the blow out. I'm familiar with the Omax.

If you're looking to outsource I know the company

Mark

 

[jimp178]

We also Drill and machine Quartz best company for drills I found in was Braemar in Texax.

We are based in Scotland Uk and had to get our drills from them for the quality, the sixes we used most were 0.027" & 0.035" but use core drills up to 1"

Regards JimP

 

[legrand01]

Thanks again for the input. I will look into the afore mentioned other companies.

Just as an "FYI" on the progress so far:
UKAM has been extremely unhelpful. Sent a couple e-mails (after phone calls) and got no response whatsoever.

I sent some parts to Micro Waterjet LLC to be test cut. They can cut the parts, but there is unacceptable chippng occuring on roughly half the parts. The chipping is occuring mostly on the ID where they are trying to blow through the small center hole. If the parts were bigger, the chips could be cut out. The final sizes and tolerances are fine for our application but the 50% fallout and the tab that must be left may prove to be the proverbal "straws that break the camels back".

They also cannot wax several layers together since the pressure from the waterjet tends to blow the plates apart.

The one good point to the waterjet cutting is that it makes for much less expensive parts (which is why the 50% fallout may be acceptable).

 

[Ceramicguy]

With the high quality drills from Lammers or Keencut you should have no problem meeting your tolerances. We consistently drill to +-.001" or better and hold concentricity within .002"FIM over 1" to 1.5" lengths. As stated earlier, a good setup is prerequisite. Let me know if you have trouble tracking them down. I'll be glad to help. You can also contact me if you wish to outsource the project.

Bruce

http://www.accuratus.com