[dalianharley]

And get away with it?

The holes are 17.8mm in diameter on the top. I do not have any 90 degree countersink bit but a 3/4-41. Will that work? The plate has 6 of these holes and are not under a lot of stress.

Thanks

Daz

[RussMachine]

We need a little more info.
Is this just to break the edge?
Is it for an 82 degree flat head set screw?
Is this part for your own personal use, or for a customer?
If a customer's print is calling out for a 90 Degree Countersink, then you'd better get them on the horn and ask before switching to 82.
A 3/4 countersink going into a 17.8 MM hole (.700) will only give you a .025 chamfer around the edge.

[dalianharley]

Here are the answers

1. It's to use with flat head screws, M8 to be exact.
2. It's metric M8 so it's 90 degrees
3. It's our own design but will be sold along with other parts as a kit.
4. The existing hole is 9mm, I just need to countersink it so a M8 flat head will sit flush in it. The top screw diameter is 15.6mm and i'm adjusting my design to 16mm.

I have 100 of these steel plates, 3mm thick, being cut by my laser shop. But they don't countersink holes. So I'll have to do it w/ my tormach (I pretty much convinced myself to buy a tormach because of this job).
My plan is to setup a 1/2" aluminum plate with dowel pins to locate the plate, clamp it down w/ some toggles and countersink with the tormach. preferably with my 3/4-41 bit so i don't have to buy a new bit...

Hope I explained better this time.

We need a little more info.
Is this just to break the edge?
Is it for an 82 degree flat head set screw?
Is this part for your own personal use, or for a customer?
If a customer's print is calling out for a 90 Degree Countersink, then you'd better get them on the horn and ask before switching to 82.
A 3/4 countersink going into a 17.8 MM hole (.700) will only give you a .025 chamfer around the edge.

[SCzEngrgGroup]

Rather than trying to kludge something using the wrong tool, why not simply buy a 90 degree countersink? They're not expensive....

Regards,
Ray L.

[dalianharley]

Ray,

I was looking into that...but for my case, countersink an existing 12mm thru hole to fit a M8 flat head (15.6mm is the top diameter) what size should I buy? Should I just get a bit that's bigger than 16mm and calculate how deep i should plunge? In my case it'd be 8mm but then the tip is flat, that'd be another calculation...is that how you guys would have done it?

Rather than trying to kludge something using the wrong tool, why not simply buy a 90 degree countersink? They're not expensive....

Regards,
Ray L.

[SCzEngrgGroup]

With a 90 degree countersink or chamfer, the depth will equal 1/2 the diameter at the top surface of the part. Any countersink or chamfer with a diameter larger than that will do the job.

Regards,
Ray L.

[TurboStep]

Why not just chamfer the inside with a smaller 90 degree bit? Any bit over 1/4" should be large enough in 3mm plate.
Step

[Hirudin]

I agree with the "why not just buy the correct bit" sentiment, but I don't think it would be the end of the world to just use the wrong tool. I created the attached image to help you with your decision.

[edit]Oops... I made the plate 1/4" thick instead of 3 mm. I'm fixing that right now...[/edit]

[edit2]Now that I made the thickness correct I don't think that size screw will work with that thickness of plate. Well, maybe low-profile screws would work.[/edit2]

[twocik]

Totally agree, buy the correct tool. I just went thru 60 plates of Ti and my KEO bit is still rockin.


KEO #4-1/2 Combined Drill & Countersink - 82 degree HSS RH 82 deg Plain: Amazon.com: Industrial & Scientific

[dalianharley]

wow, I didn't know they're that cheap. Thanks a lot for the amazon link.

The part looks awesome. hopefully i'll get there very soon!

Totally agree, buy the correct tool. I just went thru 60 plates of Ti and my KEO bit is still rockin.


KEO #4-1/2 Combined Drill & Countersink - 82 degree HSS RH 82 deg Plain: Amazon.com: Industrial & Scientific