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Countersink bolts and cutter

Rob50lx

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I'm working on a project where 14mmx2.0mm, Class 12.9 countersink flat head bolts work well for me and be used for suspension components. I don't know what cutter to order for the 6 holes I would need to countersink in 1/4" A36 Plate with 9/16 predrilled holes. I would be using a cordless drill. Which cutter should I purchase?


Here are the specs for the bolt.

bolt specs.jpg


Do I need this one?

large countersink.jpg


Is there a better choice?

choices.jpg
 
Head diameter is 30.8mm which is about 1.22" so those 1" cutters aren't going to get you flush.

HSS would *probably* survive 6 holes in A36, but cobalt isn't that much more and would be better.

I cringe at the prices, but mcmaster has 1.25" and bigger that would do the trick. I'd go with the 6 flute


Click image for larger version Name:	counter.JPG Views:	0 Size:	93.6 KB ID:	296913
 
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You want a cutter diameter bigger than the head size to get to flush. I wouldn't want to try indexable carbide in a hand tool, carbide doesn't like less than rigid setups and hand tools are the opposite of rigid. You don't want to go more-bigger than you have to or holding onto it will be difficult and cost will get insane fast. Match the angle (you already got that). I'd shop for single or zero flute in this, they're less chattery and easier to hold onto IMO.
Try travers.com for better deals and selection, price shop them against msc.com as well.
 
Looks like your countersink depth is going to be deeper than the material thickness (for flush fit).
 
You won't be able to get it flush in 1/4" plate. The head thickness is 8.4mm. 1/4" plate is 6.3mm thick. Either you go with 3/8" plate to leave a bit of meat for the bolt body or you don't countersink it flush.

The head angle is not meant to hold the bolt in shear. Even with 3/8" plate that only leaves 1mm of shoulder support for the bolt.

Edit: Just like ebs said
 
Alternative, you could probably get this to work if you go nice and slow and use lots of lube. Just like prom night. :eek::confused::eek:

As a bonus, I think the inserts are neutral rake so you'd get 8 sides to fuck up. It'll probably chatter at slow speeds. Take most of the cut slow and then finish it at high speed.


https://www.amazon.com/HHIP-2001-00...able&qid=1612396686&sr=8-4&tag=91812054244-20


No fucking way in hell the insert on that survives if you're using a handheld drill.
 
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I had to do something similar for 4 bolts and realized on Saturday afternoon that the angle was 90 and not 82...crap...

So i took a big old S&D drill bit and re-ground the point of it to 90. i would grind a little, check with combination square, grind some more, until it was the correct angle. Then i clearanced the back side of the cutting edge and it worked perfectly. when finished, i marked it as 90 degree and put it in the drawer with my cutting tools for my milling machine.
 
I had to do something similar for 4 bolts and realized on Saturday afternoon that the angle was 90 and not 82...crap...

So i took a big old S&D drill bit and re-ground the point of it to 90. i would grind a little, check with combination square, grind some more, until it was the correct angle. Then i clearanced the back side of the cutting edge and it worked perfectly. when finished, i marked it as 90 degree and put it in the drawer with my cutting tools for my milling machine.

Drills make horrible countersinks. If you hit it with that before your drilled the hole it would work much better.

I would look for a helical flute CS. Much less chance of chatter. Low RPM, LOT's of pressure and some lube.

0502221-21.jpg
 
This is very confusing, It looks like I have 2 options but the one from MA Ford would require a new drill with 5/8 chuck.

I did final a M14 x 2.00 80mm bolt with a 27mm head that would work for track bar.
I need the longer 100mm bolt with 30mm head for the control arms.

MetalCloak used this for their rear track bar and it isn't completely CS.

I thought about buying some weld/repair washers so I can fully CS.


This one has 5/8" shank
635 shank hss.jpg


This one has 1/2" shank
500 shank.jpg



Example of MC Track bar bolt not flush.
20210205_161507.jpg
 
I don't like the multiflute ones, I just don't have a strong enough spindle to use them bigger than about 3/8" OD

get the single flute one, while I like zero flute ones too, they have a limited range where the big single flute ones can be used right on down to tiny machine screws.

I don't get the worry about the shank not being on the plate, just countersink it assembled, then take it apart and countersink the mating part a little bit further so that the screw's head isn't bottoming out in the wrong piece.
If the shank is doing anything, then the bolt is loose and your shit's fucked anyways. Like bolts through rod ends or bushings, it doesn't need to be a zero-clearance fit, if the shank's in shear it's already fucked.
 
Last edited:
HSS would *probably* survive 6 holes in A36
what
a36 is bubblegum soft hot rolled mild steel that can't even get hard
HSS will live just about indefinitely long as you're keeping it at a reasonable surface speed
 
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tried one of these. had it in my mag drill and coukldn't get it to not chatter

Lots of pressure and as slow as you can go. Mag drill might not spin slow enough. I haven't tried them yet, but I've seen several people have good luck with them. Every time I buy a used tool box or auction lot I seem to find a handful of countersinks and never manage to wear them out so I haven't had an excuse to buy an insert one.


This is very confusing, It looks like I have 2 options but the one from MA Ford would require a new drill with 5/8 chuck.

I did final a M14 x 2.00 80mm bolt with a 27mm head that would work for track bar.
I need the longer 100mm bolt with 30mm head for the control arms.

MetalCloak used this for their rear track bar and it isn't completely CS.

I thought about buying some weld/repair washers so I can fully CS.


This one has 5/8" shank


This one has 1/2" shank



Example of MC Track bar bolt not flush.

Is that similar to what you're trying to do? I really don't see why they used that fastener there. A flanged bolt seems like it would be way better.

Welding a washer or solid disk before you drill seems like it'd be a good way to get more depth on the countersink. Definitely wouldn't hurt.
 
I found a good deal on a couple of them from Ebay. I'll be curious how it turns out.
 
I had good success with the countersinks I purchased from Ebay as NOS or gently used. I started with the 3/4" bit and alternated between the 1 and 3 flute 1 1/4" bit to get what I needed. It cut best when the cordless drill was slowing down as battery was running out. I used a thick washer to give me extra material.

20210213_145447.jpg
20210213_145230.jpg
20210213_145357.jpg
 
With that much surface area, rpm is the killer. As you found, applying the trigger and using the slowing motor is the best way to get it even.
 
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