Chart

I need to drill holes and tap threads in the stainless steel backing plates under the floor for my new bolsters. Stainless steel is hard, and I've never made threads before.

Is there a special kind of tap used for stainless steel?

formula31

When you drill, keep the speed down and push, dont let the drill bit drag. Use a lubricant or at least water to keep the bit cool. Taping, go slow, back the bit out regularily to clean it, use lubricant, tap magic is the best but wd40 works too. Go slow, keep the tools clean and lubricated, stay straight and youll be fine. Dont use junk bits or taps, I always use the best, coated bits and taps I can find. New ones.

Steve_H

what formula31 said.
your backing plates are probably no thicker then 1/4" and your threads are probably 1/4"-20 or 5/16"-18?
you shouldnt have any trouble tapping them but once you get the threads started straight , rotate 90° in , then back out till it frees up , then repeat.
piece of cake. any kind of oil will work ok for what your doing.

Chart

I believe you are right about the thickness of the plate, and while I've not bought the bolts yet, you're probably correct there too. Thanks for the info. This does not sound like it will be too hard to do.

jaroot

Stainless isn't TOO bad.. but once you put heat into it... then it;ll get HARD... slow on the spindle speed with a lot of coolant... cobalt drills will last a lot longer than HSS.

to tap straight take a block of aluminum that is an inch thick and square... drill a hole in it (preferably with a drill press) that is .5 mm (.020 inches) larger than the thread diameter you are tapping... lay it on top of the holes you drilled... and run your tap through it as a guide to keep things perpendicular to the surface... works for drilling holes straight also but at 1/4 inch thick it won't matter... just don't cut the holes too oversized when drilling by moving the drill around...

good tapping fluid and when it gets hard to turn back it up to break the chip then proceed forward... use a quality tap...

JR

Cord

iTrader: (2)

Stainless isn't bad-if you have a sharp bit. I've been using HSS bits that I ground to 135 degrees with a split point. Cut's it like butter-even dry. Tapping is another story. Even oil HSS taps only last for 20 some holes. Just practice on a scrap piece first. On occasion I'll get a hole that will strip from the tapping process. The final option is that you could send me the pieces and I'll put nutserts in them for you.

robyw1

You should use cobalt or better bits keeping the rpm down and LOTS of water solubale oil. Use the bounce method to break off slag because if you don't it can get clogged up in the flute of the bit and actually increase the diameter of the hole you're drilling.

Tapping really should be done with a slow RPM press if you can. You must keep it straight and be sure to go slow and stay clean

Roby

Liberator21

Use a cobalt bit, lots of coolant, and you might consider getting a tap made for stainless. Check here: http://www.besly.com/modtaps.htm

Chart

This is great guys! Cord: I'd gladly accept your offer, except the plates are glassed to the underside of the floor. As such, I'm stuck using a hand drill for the holes, and a T handle for the threads. I'll try to use the 1" alum. plate idea for a guide, and can drill that hole on my drill press.

I'm looking at the besly site for taps, and it appears they have several options for SS. Any suggestions or favorites?

Liberator21

There's a contact link on the Besley site. Email them, and ask them what to use for your application. Also, you can go to: http://www.mscdirect.com
They have cobalt taps as well as many others.