Tap Threading Newbie Question

On 06/07/2013 17:56, Alan Dawes wrote:
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Hi Alan, thanks for the reply.
Peter mentioned the correct tap for the dremel collar is actually 18mm by 1.5mm, so that throws into question the source I found that stated 3/4" 12TPI. However, since I already have the 3/4" 12TPI tap, I want to give it a try in some scrap wood first and see how it holds. Bit of a cock up on the wrench front, so am still waiting on delivery of that to try it!
That's an good idea finding an existing nut that fits on the Dremel - not sure I've seen them that large before but actually, on a similar note, I have a cheap Dremel copy which appears to have a similar collar and since that is effectively going in the bin, I could pinch the collar off that and embed it into some wood.
By the way, the perspex I am using for the router basue and was also considering using for the bit the Dremel screws into is 10mm thick, so quite hefty stuff, i.e: it doesn't look like it'd readily crack!

On 08/07/2013 21:00, Bigus wrote:
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1/2 inch by 12 TPI is far removed from 18mm by 1.5mm pitch. Translated into imperial it comes to 0.709 x 16.9 TPI. It occurs to me that as Dremel is an American device the thread might not be metric either.
Henry

On 09/07/2013 00:06, Dragon wrote:
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I see. Well, luckily the 1/2" 12TPI did the job nicely.

On 13/07/2013 13:19, Bigus wrote:
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I eventually made the effort to go and check my mains powered Dremel and found that the collar is 3/4" x 12 TPI. I guess there must be variations.
Henry

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Even though they are now owned by Bosch, they started off as an American company, so 3/4"x12tpi is not an unreasonable thread.

On 08/07/13 21:00, Bigus wrote:
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I've probably got a few in my workshop.
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Why?
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10 mm? That's a lot thinner than I was imagining you'd be thinking of using.
Perspex is prone to developing cracks where there are sharp inclusions, and the act of tapping will produce them in profusion. Routing would cause just the sort of strains which would start cracks running.
I'd be tempted to try to find some hard-vulcanised rubber.

On 09/07/2013 01:27, RustyHinge wrote:
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The tapping into the perspex went very smoothly and the Dremel screws into the hole without being too tight but is nevertheless secure. I'll see how the durability goes and try some hardwood or vulcanised rubber if it fails.
My main problem is cutting the perspex. I am using a scroll saw and tried to cut a v-shaped chunk out of it but it melts the plastic and causes it to fuse back together just enough so the cutout wont detach from the main piece. My attempts to extracate it caused the whole thing to crack, but then I got frustrated and used a chisel! I can't use water in this application as it'll go into the scroll saw unit.

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Any power tool (saw, mill, drill,) will melt Perspex unless you can reduce the speed drastically or cool the cutting zone. Cutting by hand is the simplest solution, but even then care must be taken not to overheat the plastic. Add to that the problem of stress cracking and it would be advisable to seek a more forgiving material. You only make things difficult for yourself by persevering with Perspex.
Cliff Coggin.

On 13/07/13 13:33, Bigus wrote:
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Cut it with a tenon saw, a panel saw or a hacksaw - using water...

On 13/07/2013 21:32, RustyHinge wrote:
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A large hacksaw made light work of it thanks