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I have an el cheapo 10" table top drill press. Does anyone know if the motor can be slowed down with some kind of rheostat without burning it up?
Thanks.

Brian

It is done with belt pulley sizes.The slower the better for your bits.You do have a pulley on the motor and one on the spindle,don't you ?? A rehostat is not a good idea.

Yes of course the press has pulleys and it is set for the slowest speed right now, 540 rpm, which is too fast for drilling thick steel. I'll have to try find a larger and smaller pulley combination to slow it down.

Brian

Brain's40,

It would be nice if this could be done, but it can't. As gtow69 pointed out, gearing would be the only practical way to do this on your small drill press. The larger the drill bit, the slower you turn it...you must want to drill a large hole.

The AC motor will lose torque when you slow it using electrical means, while a sheave reduction will up the torque proportionately.

Small AC frequency drives are available that allow nice variable speed features, but sticking one of these on a small, cheap drill press might not be the best move.

Stuart

Brain's40,

Keep in mind the RPM of the drill is not dependent on the thickness of the material to be drilled, but on the diameter of the drill(generally speaking).

If 540 was the appropriate RPM for a 1/2" HS drill in A36 steel, the hole could be 6" deep...makey-no-diff!

The larger the drill diameter, the more SFPM the drill travels in one rotation, and this is the critical factor.

I have a real simple formula for figuring drill RPM based on drill diameter..it's down in the shop, and I ain't. I will bet someone else has that info and will be along shortly.

I wouldn't feel nervous about turning a 1/2" bit at 540 RPM in mild steel...use a liberal amount of Rapid-Tap, or any coolant or cutting fluid.

When the chips come out bright red and stick to your cheek, it's time to back off!

Stuart

Formula is:
cs x 4 /d = rpm. If cutting speed is 80 sfm (ok for mild steel) then 80 * 4 = 320 divided by drill diameter(.5) = 640rpm

Curt B.

Thank-you for the information Stuart and Curt. I guess what I need the slower speed for was for a little more control. For instance I replaced the bushings in my clutch and brake pedals. The original holes I believe were 13/16 and my replacement bushings were 7/8 o.d. I know that a reamer would have been the tool to use, but I drilled them out to 7/8. It worked OK but I just felt that I could have done it more accuratly if the drill wasn't spinning as fast as it was.
Thanks again.

Brian

Brian,
You are correct, 540 rpm is too fast for drilling a 7/8" hole in steel with a standard HSS (high speed steel) drill bit.
Years ago, when I bought my drill press, I was looking for one that would go as slow as 300 rpms or less. I ended up buying an inexpensive model made overseas (Taiwan) that has 16 speeds ranging from 215 to 3250 rpm. I have had this drill press for more than 20 years, and it works fine. I have drilled holes up to 1" in mild steel without any problems. As mentioned above, I use cutting oil, when drilling steel. Mine is a 3 pulley model. That is most likely what you will need to have, to go that slow without having to use a very large pulley on one side and a very small one on the other.
Also, as mentioned above, it is not so much the thickness of the material that matters, but the type of material, type of drill bit (high speed, carbide, etc.), and the hole diameter that you are drilling.

If I were you, I would look for another drill press. Or do your heavy drilling on someone elses.

Good luck

John

Coolant.