[will gilmore]

Has anyone tried or succeeded in using a used granite or steel surface plate as the base for a machine tool? I saw this on ebay:

http://cgi.ebay.com/Starrett-B-Cryst...QQcmdZViewItem

It has fixtures on it so its obviously possible to put fasteners in to it. Heavy, good vibration damping, flat. Anything I'm not thinking of?

[ironDigit]

I guess steel would be easier to custom drill for mountings and stuff but great base if you got one lying around.

i even saw one of them fancy diam measuringstations transformed into a minilathe.

good luck.

[will gilmore]

I don't have one laying around but a few hundred dollars for a nice flat base seems like a deal. You couldn't buy accurately ground steel or aluminum for that price.

[JMcDonald]

I wouldnt use granite to actually build a mill off just for the difficulty of machining mounting surfaces. If I found one that had rows of mounting points (maybe drilled / tapped holes), Id consider it. Then again, that would probably be really expensive, so maybe not, heh. Were I to build a new base, it would probably be made of bolted-together steel plates or bars, and possibly filled with concrete and / or some other filler.

[will gilmore]

I was thinking of drilling the granite with some kind of masonry drill (not sure how easy that would be) and then epoxying in some threaded inserts.

now that i said that it sounds like more trouble than its worth

[JMcDonald]

The only way you could really do it would be if you had a mill big enough to do the machining on the entire base.

[will gilmore]

well the advantage of the surface plate would be that you wouldnt need to flycut or surface the whole thing in one pass. you would just need to accurately drill which i could probably do in my bport

[JMcDonald]

Yeah you should be able to do a decent sized surface plate on a mill like that. Were I to build a mill, Id probably use maybe an 8x24 plate, mounted longitudinally to support the y-axis. That should be easily machinable with a big vertical mill.

So, since you do have a machine like that, I say go for it if you can find the right sized granite plate!

[will gilmore]

anyone have links to drilling, epoxy, inserts for granite? someone must have already figured this out for fixtures on surface plates

[ironDigit]

If your going to buy a surface go for a cast-ironplate and drill&tap on the Bport ,that sounds wonderfull from over here.

I once contemplated : a large*ss 3x3foot surface plate and have some1 with a "portable" gantry-style router do the layout engravings for all the mountingholes whilst having it set-up as the 3x3foot surfaceplate was the actual table and the gantry cutting into itself to afterwards de the drilling with a magneticbaseDrill.It still sounds good to me but then the surfaceplate was snatched( i was overbidden) and i never looked back.

with some luck you'll come acoss a closeby angleplate on e-boy or alikes to make you up a real nice'n easy Z-column.

i'ld say lead the way and i might very well follow as i'm starting to get close to the stage of composing meself a base for the screws-n-slides i've collected sofar.

BTW i'm kinda itchy bout the granite after all i heard about cracking plates and molten drills and trying to accurately epoxy treads into the created holes seems asking for it.

Good luck.

[lgalla]

http://www.granitecitytool.com/showi...=88&mcatnum=92
http://cgi.ebay.com/18-X-24-BLACK-GR...ViewItem<br />
Larry

[ironDigit]

made me wonder if the ironsurfaceplates won't warp after drilling lots of mountingholes.

Hope someone can chime in on this.

I'm quite confident that this won't be of any concern when granite is used.

[will gilmore]

here is another thread with some good links about inserts and epoxy

[will gilmore]

oops here: http://cr4.globalspec.com/thread/775...-Granite-stone

[Mcgyver]

made me wonder if the ironsurfaceplates won't warp after drilling lots of mountingholes.
.

you will be fine drilling it, cast iron is generally very stable - one of the properties that makes it a good choice for surface plates and machine bases. unless its a junk plate to begin with, a cast iron plate would have been stress relieved/seasoned and there just isn't the equilibrium of stresses you get with steel or a steel fabrication.

[NEATman]

As for drilling granite, we have done it in our shop with a drill press. You need a diamond core drill (like this one: http://cgi.ebay.com/1-1-4-Diamond-Co...QQcmdZViewItem)
and a big lump of clay to creat a "moat" around the hole to fill with water to cool the bit. The trick is that this is a hole saw, not a drill. Once you get to the desired depth, you snap off the core with a flat bladed screwdriver.

The other tricks are:
Roughly lay out the holes on the granite, and drill with a small drill press sitting right on the granite. A $60 import works just fine. Bond in the steel inserts - without any tapped holes in them. Then accurately layout your holes on the inserts, and drill and tap the steel. This can be done with a sheet metal template, or on a large milling machine. The tapped don't need to be perfectly concentric to the inserts.

Also, a trick for getting the inserts just below the surface of the granite is to put a piece of tape over the top of the insert, and trim it to the OD. Then get a magnet that is wider than the OD of the insert, stick it to the insert over the tape, and plunge the insert into the hole that is partially filled with epoxy. The magnet holds the insert the thickness of the tape below the surface. When dry, remove the magnet & tape, and you should be a few thou under the surface every time. If you make the inserts a tight fit in the cored holes, you'll need a vent groove or flat in the side of the insert. You may also want to make the insert with a "spool of thread" profile or sandblast the OD to give the epoxy something to grip to.

NEATman

[ironDigit]

inserting blanks and tap after epoxying 'm in place.......

i guess it just takes a genius to be genius.

would a surface flat to 0.07mm be flat enough to fully advantage thk style lineair ways and ballscrews ?

[NEATman]

ironDigit-
Thanks- It wasn't my idea initially. I forget who told me about it. It's a great trick.

I've designed at least 20 machines with granite bases. Starrett, Rock of Ages, Tru-Stone, etc. will all add inserts to granite for you. The craziest one was a piece of black impala granite quarried from South Africa, brought to Barre VT (Rock of Ages), and cut, ground and drilled there. It was 36" wide, 30" thick, and 240" (20') long. It weighed in at about 26,000 lbs. They ground and lapped the top surface flat to .0007" over the full length! It had loads of inserts epoxied into it.

Regarding .07mm being flat enough for THK rails, it all depends on how accurate of a machine you want. You may feel some drag or binding if you have a very stiff piece of metal connecting the bearing blocks. Depending on what style rails you have, and over what distance, etc. will all effect the feel of the rails. Some are more forgiving that others. Check thier website to find the min. reccomended flatness for your rails. http://www.thk.com/technical/seihin_en.html

NEATman

[will gilmore]

wow these are a lot cheaper than I thought.

http://www.use-enco.com/CGI/INSRIT?P...&PARTPG=INLMK3

It would be a lot of work to mount all the rails, ballscrews etc. I'd like to build a small cnc lathe. I think 24x18 would be a good size for a base