Drilling Granite

[tootalew]

I just threw away over $100.00 in diamond drill bits trying to drill through a granite surface plate. I bought (2) 1/4" bits ...

First
http://www.granitecitytool.com/showi...=88&mcatnum=92

Second
http://www.ukam.com/webcatalog_drills_ordering.htm

The bit from granite city has 8000 rpm printed on the side, and the highest rpm my press will go is 3850. So I mount the water swivel and the bit and turned on the drill press. It was so off balance, the chuck came off its taper. So I removed the swivel and just went with an adapter. I did not want to dry drill so I cut a pice of pvc tube and used it as a moat to hold water. The first inch was great, and I thought this would be a piece of cake. After the first inch it stopped drilling so nice, so I stopped and cleaned the bit with a dressing stick (from ukam). Still nothing, so i pulled the bit out again, and it looks shot. So then I tried the bit from ukam and it lasted all of 30 seconds and not even a hint of diamond left on the bit at all. That was the $60 + bit. The grainte I am drilling is pink with a high quartz content.
I called granite city and Kent told me that black surface plates are very soft and drill much easier. This is for the base of a lathe, which is why I am posting this here.

My local counter top wants almost $400.00 to supply me with a piece of 1 1/4" granite 9" x 20" with a total of (20) 3/8" holes drilled through (the smallest they can drill is 3/8").

Back to the drawing board.

[tootalew]

Went back to drilling again this afternoon, I had a 5/8 diamond core that I planned on using on the back side as a counter bore. This time I had no problems drilling, but got some ugly blowout on the bottom side, more than I would have thought. So maybe drilling 1/4" holes through 2" of granite is not a good idea. The plate I am drilling is not what I intend on using for the lathe, but it has given a bit of practice. I did find a surface plate on ebay today, and when I bought it I thought it was granite, I may be wrong.

http://cgi.ebay.com/ws/eBayISAPI.dll...%3DI%26otn%3D1

I am thinking this may be a ceramic surface plate. If it is ceramic, would it make a good lathe base? Can you drill ceramic?

[emd68]

tootalew,
I looked at the surface plate on eBay. It looks ugly but I would assume that it is granite, I have never seen or heard of one being made of ceramic. If you think your having a hard time coring or drilling granite the ceramic would really drive you up the wall. I think the problem you are having with drilling is at first it goes fast because the swarf comes out of the hole because it is shallow but as you get deeper into the material the swarf can't get out and you can't get enough coolant in so the cutting edge heats up and dulls the diamond. You also said the core drill from ukam looked like the diamond was gone after 30 seconds, I would guess that it was a plated drill which is useless for you application. To help minimize blowout on the backside of your surface plate there are two things you can try. First put a piece of plate glass under the granite say 1/4" thick. Second try backing off on your downward pressure for the last 1/8"-1/4" of material.

Hope this helps
Ed...........

[tootalew]

Ed,
I first saw a ceramic surface place at a local shop that does blanchard grinding, I did not even know that they made surface plates from ceramic. It was not solid, 4 walls and a top. Thanks for the tip on using a glass plate under the granite. I had it sitting up from the table on blocks because the without the water swivel the bits would not reach the table. What I am using as a drill press is a now discountinued drill/mill from harbor freight. It has a round coloum, so I turned it around and swiveled the head 180 degrees. I also put a drain in the table that goes into a 5 gallon bucket, a drum trap so to speak, I do not want be adding gravel into the sewage line. I also found someone over at practical machinest forum that is in the area that has some experiance in doing this.

I want to used THK tapped rails on this, which is why I want a hole through the granite, verses using inserts. I don't think I will try again with 1/4", but may go 5/8" all the way through, epoxy in some undrilled inserts, and then drill and counter bore the inserts on a mill.

[Rico55]

tootalew,
Try using a hand-held hammer drill with a carbide masonry bit. I have drilled a lot of hard substances with these (though not granite specifically). Use a high quality hammer drill and a good quality bit, and use some water as a lubricant as you go deeper. I think this will do it, and you should be able to get any size bit you want, from 1/4" to 5/8". Take a small piece of the material down to the tool rental yard and see if they will demonstrate a hammer-drill for you.

[will gilmore]

i'm planning on doing this also so im curious what your solution is. part of the job of the water (in addition to cooling) is to carry away the granite that is cut.

[tootalew]

My solution right now is ....
I went to another granite countertop fab shop, and have a piece being cut to size. I then plan on drilling 5/8" through (well the bit is 5/8, but the hole it leaves is closer to 11/16). Then I will make some tapped T shaped inserts and insert them from the bottom, with no epoxy.

[will gilmore]

let us know how it goes. i want build a lathe on a surface plate which is 3" thick so drilling is going to be an issue. how flat is the granite countertop?

[tootalew]

Just an assumption on the counter top granite, not only on my part, as I have seen others post the same assupmtion. I believe counter granite is just as flat as surface plate, and I dont think there is a whole lot of differance in the grade of surface plate, except if company says its Grade A or AA they can command a much higher price. I believe that the same machines are used to produce both. The logic behind this is that in order to mass produce either the machines have to be so heavy and tight (just to elminate chatter, or the machines would tear themselves apart), that is would be hard not to produce a product that is within say .0005" of flatness. I would to love to hear other peoples opions or known facts on the subject.

I would like to also use a surface plate, but for the parts I have aquired over the years (namley the ball screw), I need to have around 21" in length, and most surface plates jump from 12 x 18 to 18 x 24. Now a surface plate at 18 x 24 is going to be wieghing in at around 175 to 200 lbs, more than I would attept to try to get down my basment steps. I have thought about having a plate delivered to a local counter shop and cut down to size, and delivered to my house and down the stairs to my bench. I would love to have a 4" thick granite base to start off with, and rails bolted directly to the grainte.
But I think I will start off with counter remnets first and see how it works.

[lcarrudajr]

I needed a surface plate so I friend of mine took a piece of black basalt and polished it really well, and gave it to me as a present.
I cant see any diference from a comercial surface plate.
May be an mitutoyo surface plate has its uses, but not for me (for now).
Anyway, the black basalt surface plate It looks nice.

lcarrudajr

[BillTodd]

I believe counter granite is just as flat as surface plate, and I dont think there is a whole lot of differance in the grade of surface plate, except if company says its Grade A or AA they can command a much higher price.

Place a good straight edge against the surface and check for gaps using a 1 thou feeler gauge (or observing light at the interface is a another way) .

I would guess the counter granite it no better than 0.001- 0.002 over 12" (ISTR plate glass is similar). A grade A surface plate is 0.0001" over 12", and a grade AA 0.00005"


http://www.qcssindy.com/techpapers/surfplatetol.htm

Total Flatness Tolerance (Grade AA) in microinches = 40 + (D²/25), where D = Diagonal of the plate in inches. Round the result to the nearest 25 microinches. Total Flatness Tolerance (Grade A) in microinches = Grade AA Tolerance * 2

[tootalew]

Progress...what a good feeling. I have been in the planning stage on this project for years. I got the countertop granite today, and with no real way of testing its flatness in my shop, I opted for the light test. At first I was a bit dissapointed, as I could see light, from under a THK HSR rail. Then, I not only saw light, but dust, so I clean both surfaces, and there is no light. I may run out and try to find a feeler gage tommorrow.

While I was waiting for the granite over the weekend I set up the Drill/Mill to do the drilling. I found a set of IKO cross roller linear guides size 65 a while ago, so I set up on the bench and just bolted it on either end to the bench. Then I attached two sections of 2" x 4" to the guide. It worked rather nicely, I was able to drill the first row of 5/8" holes (9 holes) in only a couple of hours. After each hole, I had to stop and do a bit of clean up, as the water swivel leaks, and water was everywhere. I will let things dry out, and go at the other row tommorrow. I will attach a picture of my set up.