Moderators: Random Orbital Bob, nev, Noel, Charley, CHJ

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By Lonsdale73
#1261249
I have a 2.5mm sheet of stainless steel that I want to attach to an aluminium mitre bar that came pre-drilled with 6mm threaded holes. How do I best go about it? Can I simply drill a slightly smaller pilot hole and let the bolt cut it's own thread? O do I need to use a tap to cut a thread in the sheet? I've no idea what the pitch is of my bolts.
By Rorschach
#1261253
If the aluminium bar is already tapped you just need to drill a clearance hole in the stainless sheet. 6mm holes will do it or 6.5mm if you want a bit of wiggle room.
By Lonsdale73
#1261254
Thank you
By AES
#1261370
If it helps Lonsdale, EXACTLY what Rorschach said!
By Lonsdale73
#1261418
Rorschach wrote:If the aluminium bar is already tapped you just need to drill a clearance hole in the stainless sheet. 6mm holes will do it or 6.5mm if you want a bit of wiggle room.


Reading that again, will it make a difference that I need to screw through the bar into the plate? The bar's already countersunk and needs to be on the underside of the plate.
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By Lons
#1261423
Lonsdale73 wrote:
Rorschach wrote:If the aluminium bar is already tapped you just need to drill a clearance hole in the stainless sheet. 6mm holes will do it or 6.5mm if you want a bit of wiggle room.


Reading that again, will it make a difference that I need to screw through the bar into the plate? The bar's already countersunk and needs to be on the underside of the plate.

That's a bit different but maybe you need to post pics or a drawing to clarify.

If there's a thread in the bar and the countersunk bolt needs to screw through that first then into the plate then you will need to drill and tap the plate to 6mm to suit the bolt.
That isn't an ideal way to get a tight fix however as for best fit the bolt needs clearance through the bar hole to pull tight to the plate. 2.5 mm isn't a lot to get hold of.

Think when you screw though a bit of wood into another, unless you've pre drilled the clearance hole the screw will tend to push the 2 bits apart as it goes through similar result can happen.
By AES
#1261447
Still agreeing with everyone else if it makes any difference - this is 1 case where a picture (rough sketch will do) really is worth the oft-quoted 1,000 words.
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By CHJ
#1261449
1. Drill the bolt clearance holes in the 2.5mm plate.
2. Clamp the 2.5mm plate to the mitre bar with holes aligned.
3. Countersink the plate and the threaded hole deep enough to allow a countersink machine screw to sit flush with the plate surface.

screw.jpg
screw.jpg (4.01 KiB) Viewed 329 times
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By Lons
#1261455
CHJ wrote:1. Drill the bolt clearance holes in the 2.5mm plate.
2. Clamp the 2.5mm plate to the mitre bar with holes aligned.
3. Countersink the plate and the threaded hole deep enough to allow a countersink machine screw to sit flush with the plate surface.

screw.jpg

That's the way I would fit it as well
By AES
#1261488
Once again "me 3"!
By John Brown
#1261497
But the OP says "through the bar, into the plate". Seems to me that drawing shows through the plate, into the bar. But I guess it's all conjecture in the absence of a sketch from the OP.
By Setch
#1261499
If you already have threaded holes in the bar, drill clearance holes in the sheet and insert the screws from the other side. 2.5mm isn't much thickness to tap, but should be enough to countersink for a screw head.

**this is what the posters above said already, obviously I was late to the party!**
By John Brown
#1261515
Whatever the ultimate resolution, I think everybody agrees that tapping the holes in the plate is a bad idea.
By Lonsdale73
#1261575
Thanks all. Been sidetracked but will look at it again and get back to you.
By AES
#1261686
Thinking about your job Lonsdale, I suggest that you do exactly as CHJ has drawn but instead of tapping and using a bolt, you rivet it. This assumes that A) the plate doesn't have to rotate on the bar, and B) a permanent fix is OK.

If the plate is already tapped, drill the thread out to clear it, then countersink, but ideally use a 100 degree c/s instead of the usual 90 degree (these are common in the aircraft industry and can be bought from Snap On amongst others. The reason for 100 is because although it's ss, your plate is only 2.5 mm thick and this will make a much better flush head that won't distort the plate or break it in use).

Choose, ideally a steel c/s head rivet, or a hard "aircraft alloy" 7000 series rivet, NOT a "standard" pop rivet, and make sure it's a tight fit in the hole. Cut off the length so that when entered into the hole it's between 2 and 3 times the rivet dia above the combined plate and bar. If you're used to riveting you can form the head with only a ball pein hammer, but best is probably to buy a rivet snap and dolly to at least start & finish the head forming on the other side.

HTH.

But if the pieces are small you can send them both to me and I'll do the whole job for you as I have all the rivets and gear necessary. Your only cost would be 2 ways post, but unfortunately the Swiss PO are rather (to say the least) ridiculously expensive, sorry. The job'll take about 10 mins!

Alternatively, IF I can find it, I can send you a scan of the appropriate pages of my initial apprenticeship training manual - I think I've still got it somewhere - so you can have a go yourself - assuming you haven't already learnt hand riveting. It's quite easy once you get the knack, and really useful.