tapping threads in stainless steel
 

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?

Re: tapping threads in stainless steel
 

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.

Re: tapping threads in stainless steel
 

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.

Re: tapping threads in stainless steel
 

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.

Re: tapping threads in stainless steel
 

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

Re: tapping threads in stainless steel
 

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.

Re: tapping threads in stainless steel
 

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

Re: tapping threads in stainless steel
 

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

Re: tapping threads in stainless steel
 

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?

Re: tapping threads in stainless steel
 

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.

Re: tapping threads in stainless steel
 

Thanks. I'v now read their site, and understand the differences. Should have done that before asking in the above post.

Re: tapping threads in stainless steel
 

There are a couple of types of tap handles one has about a 6 inch long 1/4 diameter rod through it for turning and the other has two handle on it the second might be better for you to help keep the tap straight another way to help you keep it straight is take a scrap piece of steel about 1' thick and drill a hole in it the od of the tap just put this over the hole and hold it down as you start the tap it will keep it straight
All good points lubrication 3/4 turn in 1/4 turn back to clear chips

Re: tapping threads in stainless steel
 

Just curious. How thick are these backing plates, and what size holes do you plan to drill? You have to make sure you have enough meat to cut threads in.

Re: tapping threads in stainless steel
 

Cord's got the right idea. Nutserts (Rivnuts), are the way to go. Especially if the metal is a little thin. http://www.bollhoff-rivnut.com/
They can be installed in a blind hole.

Re: tapping threads in stainless steel
 

well lubed, slow with a lot of back and forth action...don't be in a hurry, if you snap the tap off....you'll need dynamite to get it out.
Good luck

Re: tapping threads in stainless steel
 

lol :D
or a tap extractor

geez guys , he isnt building a space shuttle. an old beat up tap with missing teeth can handle this job. just make sure you drill the right size hole. if you dont know ask the guy at the hardware store to look at a chart........Chart :p

Re: tapping threads in stainless steel
 

lol
I was wondering when some one would come clean
once you do it you will realize it is easier then starting this thread

Re: tapping threads in stainless steel
 

Was that overkill?.......What is the atomic weight of salt, let me see................

Re: tapping threads in stainless steel
 

I'd say its more tough than hard.Sharp tools and don't force tap if its dull.

Re: tapping threads in stainless steel
 

Stainless is gummy, tough, and abrasive.

Need cutters with sharp tips. Need low rotational speed to keep heat down. Need constant chip thickness to keep cutter from chpping.

Thread cutting oil (or gear oil) is necessary when tapping stainless.

No biggie.

Re: tapping threads in stainless steel
 

This is good. Thanks for the advice. I've gotten the tap (and a spare), and hope to get to this stage of the project in a few days. Will report back afterwards.

Now, the tap has a funny square end on it... think Vice Grips will hold it? :D

Re: tapping threads in stainless steel
 

Hehe, hope you were joking. Use tap handle only.

Re: tapping threads in stainless steel
 

Yeah, I was joking. That's about as good a joke as I'm capable of telling. :eek: :rolleyes: :D

Family thing has come up, and I'm going to have to leave town. This delays installing my bolsters, but I will report back afterwards. Thanks again, all.

Re: tapping threads in stainless steel
 

Why don't you just through bolt them? You'll just need one of those 6' long drill bits the electricans use.

Re: tapping threads in stainless steel
 

Jeez Cord, I thought you were brighter than that. :rolleyes: My boat is a deep v, and there is no good way to get either the head of the bolt or the nut to torque down correctly if it's not perpendicular to the surface it's compressing, which would be the bottom of my hull in this case. You guys with cats don't understand what it's like.

Besides, where would I find a 1/4-20X24" stainless steel bolt? :D