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jteef 1st October 2002 03:08 AM

working with stainless steel
 
I have been putting this off for a really long time(as evidenced by the dust in last picture :) ) because I haven't come up with a reasonable solution.

My experience with stainless steel has not been a good one. I don't suggest it as a material for anybody new to fabricating things.

anyways, a friend of mine welded the main part of my chassis together and put a nice finish on it. The problem is that my cad drawings were a bit vague so he didn't send me a top panel, a bottom panel or a back panel. I got him to make me the required panels at a later date, but they weren't drilled and didn't include any hardware etc. I wanted something fairly decorative to hold it together, so I bought some stainless steel sheet metal screws. Drilling the pilot holes was a real pain. I went through 5 cobalt drill bits to get about 25 holes. Also, the drill press liked to "walk" a few millimeters away from the intended hole which led to misalignments and scratches.

Anyways, I went to screw in the sheet metal screws, but they just sat there and spun until the threads melted... I tried widening the pilots, using lots of force, high speed, low speed, etc. That plan just wasn't going to work. So I went and bought #8 stainless machine screws and nuts which took care of the bottom and the rear panel. Now I'm stuck on what to do with the top panel. I will need some way of removal so gluing isn't an option. I tried some tek screws which are a screw with a drill bit, a self-threading "spike", and then the threads. The one I tried did work, but it was zinc plated and had an angled head which makes it stick up about 5mm. Basically really unattractive.

so, I am asking if anybody has ever seen a Tek-screw made of stainless steel with a head that will mount flat against the surface. If not, is there any kind of epoxy or glue that I could use to secure a nut in place on the bottom of the cover that would have enough strength to let me tighten some machine screws?

I have some pictures at:
http://heracles.cuties.org/~jt/leachamp

thanks

jt

Peter Daniel 1st October 2002 03:30 AM

2 Attachment(s)
So the holes are too big already and you can't tap them in regular way?;) I never use those self tapping screws, and on stainless still it's a road to ruin.;)

You can either enlarge the holes, use proper tapping technique and install machine screws or use so called blind rivet nuts or panel nuts. McMaster has a decent selection of different kinds. Home depot does not seem to carry them in their hardware section.

They might be hard to install in stainless steel thou. You push them into slightly smaller holes and because of the teeth (they have) they should stay in place.

roddyama 1st October 2002 03:32 AM

JT,

You could make some long stand-offs that go top-to-bottom inside the top and bottom lips. Tap both ends of the stand-offs to what ever machine screw you want. It may be a bit of a hassle getting the last panel holes to line up, but you will be able to tighten them without a problem. (Donít make the stand-offs out of SS)

Rodd Yamas***a

jteef 1st October 2002 04:55 AM

Those press in things look like they could work. I don't think the panel is thick enough to tap. <1mm. If it is, I don't think it would last for more than a couple of removals and tightenings.

looks like the smallest package is 100 of them @ $10.76 + shipping. But since I am fairly positive no hardware store in 150 miles will have anything similar mcmaster sounds like a winner.

how do these work? Do you just tap them in with a hammer?

thanks

jt

Peter Daniel 1st October 2002 05:51 AM

I prefer to push them in with a vise or clamp. They work perfect in aluminum, don't know about stainless steel. Very important is the proper hole size, not too big and not too small.The best way is to experiment on a piece of scrap metal to get the feeling. That's what you should have done with your Tech fasteners.;)

I have some of that blind nuts at home, but only in #6-32 size. If the size is right, I can send them to you.

It would be still possible to tap proper thread in 1mm stainless plate. It's very hard material and it should last. When you drill holes next time, use slowest speed and lubricant.

jteef 1st October 2002 06:34 AM

My holes right now are 3/16"

I will try tapping tomorrow before i buy anything. I hope my friend with the tools has done it before :)

jt

Peter Daniel 1st October 2002 06:39 AM

3/16" is pretty big. Use lubricant, it helps a lot (even W40 or any oil is OK).

mbroker 1st October 2002 11:38 PM

Looks pretty nice, so far!

To aid drilling holes in metal, use an awl or center punch to make a small divet where you want the hole. The bit will not walk, then :) But it looks like you tried this? Hit it harder, next time! ;) Also, *always* use some form of oil when machining metals, including aluminum. The thinner stuff (WD-40) is usually better. Also, some cutting fluids will react with aluminum :eek:, so be sure you buy the right stuff! Oil/cutting fluid will *drastically* aid in machining so you won't go through so many bits.

The smallest screw you could tap for is a #12, next is a 1/4". Either will work fine in thin material as long as you don't overtighten them. There are plenty of fastener choices at Fastenal, and I'm sure you could find short stainless flat head 1/4-20's. Peter's nutsert is also a very good idea, and I'm sure Fastenal will carry some of those. The last time I ordered from Fastenal (about 18 months ago), I was able to order individual pieces, too.

Good luck and good job! :up:

Mark Broker

jteef 5th October 2002 01:02 AM

I tried tapping this afternoon with no success. I was using an 8-32 tap which looks very close to the holes that I have drilled already. The taps were fairly dull near the tip so i'm gonna go to lowes tomorrow to see if i can get a single part rather than a whole set.

maybe i'm not using them correctly though? I sprayed the hole and the tap with some WD-40, then put a moderate amount of force down while screwing. I could get bite for about a 1/8th-1/4 turn, and then the tap would come free. Are there any jigs or whatnot that aid in getting the tap in straight? I can see how this might become a problem. Right now i'm using a handheld "key" that the taps fit into. similar to the chuck on a drill.

Thanks

jt

Peter Daniel 5th October 2002 02:14 AM

For 8-32 tap you need to predrill the hole with 9/64 drill, no more, no less. Stainless steel is pretty tough so you go as much forward with a tap as you can, than back up, clean tha tap and go again untill you done. Handheld key is OK, but it's hard to keep it straight. I much prefer to use cordless drill gun with adjustable clutch. You can't go wrong this way and it's much faster. It's enough to put oil only on tap and not hole.


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