Countersinks angles

This topic has 8 replies, 5 voices, and was last updated 19 February 2012 at 20:03 by pgrbff.

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27 January 2012 at 19:43 #83213
pgrbff
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@pgrbff
What angle countersink do I need for an M3 countersunk machine screw? Most seem to be 90 degree.

Any sugestions on the best type of countersink to use on carbon/glassfibre sheet which I need to attach to an aluminium frame. I believe the general rule is highest speed possible with carbon fibre sheet.
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27 January 2012 at 19:43 #5899
pgrbff
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@pgrbff
27 January 2012 at 20:01 #83216
Anonymous
Most British countersunk screws have head angles between 90° and 92°, so a 90° countersink will be fine.

Personally I use three flute countersinks; they seem to cut well without chatter. Both fibreglass and carbon fibre are abrasive, so ideally a carbide countersink, but if you’re only doing a few then HSS will be fine. I’d limit the speed; if you go too fast you’ll end up softening the resin, and countersinks seem more prone to chatter at higher speeds..
27 January 2012 at 20:33 #83223
pgrbff
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@pgrbff
Thanks. I only have 4 holes to do.

At such a small size I imagine there won’t be much time for the resin to overheat as long as the tool is sharp.
19 February 2012 at 16:22 #85248
pgrbff
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@pgrbff
I enjoy the challenge of making parts for my model helicoters and have had great help on this site with learning how to perform simple engineering tasks. My problem is that whilst I enjoy the practical side, I don't have my own machines and rely entirely on using a neighbours workshop. Add to this that I usually end up buying my own tooling and large pieces of stock, it works out extremely expensive. What is the best way to find a small workshop that is happy to perform small jobs? The drawing below is an example of the type of parts I need.
19 February 2012 at 16:31 #85250
elanman
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@elanman
Hi,

For work on carbon you need a carbide or better still a diamond cutter as HSS has a very short life. Another way I have found OK is to make a solid point on a piece of MS or alloy bar and super glue some wet and dry abrasive paper to it. It does not last long but it's cheap and the paper is easily replaced. When counter sinking I use a hand brace, that's fast enough.

Cheers

John

Edited By elanman on 19/02/2012 17:02:12
19 February 2012 at 17:06 #85255
Another JohnS
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@anotherjohns
All metric countersunk screws should be 90 degree.

You might find that the North American screw threads are 82 degrees; although I live where the UNC/UNF reign supreme, I use solely metric, so don't quote me on other threads, like BA and ME!

I generally use a 90 degree countersunk; most of mine are about 6 flute. Take it slowly for metal, the cutting surface is rather large. (don't know about fiberous non-metalic surfaces)

In theory, you should have a countersink that matches the OD of your screw head so that there is a very slight parallel where the widest part of the screw head is, so that the screw head goes flush, but the countersunk hole does not look overly large. I generally just don't bother worring about this part!

Another JohnS.
19 February 2012 at 17:53 #85257
KWIL
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@kwil
pgrbf,

Even if you can find a "local" jobbing workshop, you will still be paying for minmum purchase of material to suit your job and also be paying their overhead costs (wages, rent, tooling etc), so I doubt it willbe cheaper for small jobs.

K
19 February 2012 at 20:03 #85266
pgrbff
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@pgrbff
If I could find somewhere local I'd be happy. I can't!

Even if tools and materials are relatively inexpensive, a company like MSC charges £10 for delivery to Ireland. So if I need a 2.05mm jobber, and can't get one locally, ordering from UK costs a fortune.

I'd rather give the money to someone who knows what they're doing and not have to worry about when my neighbour will have time to help me out.
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