Slightly sizing down a carbide drill


Page 1 of 2 12 LastLast
Results 1 to 12 of 14

Thread: Slightly sizing down a carbide drill

  1. #1
    Member
    Join Date
    Nov 2017
    Location
    United States
    Posts
    399
    Downloads
    0
    Uploads
    0

    Default Slightly sizing down a carbide drill

    I have a job that will need about 150 holes drilled in 3mm thick carbon plate. The holes need to be 4.33mm +/- .01mm. It's right between common sizes of 4.3mm and 4.365mm. Normally I get my carbide drills for these jobs from drillbitsunlimited for just a couple bucks a peice and they work great. I found a couple 4.33mm elsewhere but they are around 25 bucks and hss. Could I possibly grind a 4.365 down to 4.33? Was thinking maybe just chuck it up in my cnc and slowly step into a grinding stone in my vise. Only needs to drill through 3mm, so only a small portion needs to be ground. These drills are only 10mm long flute to begin with so it should have good rigidity as I rub it up against the stone. Will it work?

    Similar Threads:


  2. #2
    Member Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    3419
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    First I think I would go back to the engineer and have a chat, maybe a more standard size would work. It seems a bit strange that the spec would be an odd size.

    The odds of a hole being drilled exactly to the bit size is small at best, drilling is a roughing operation. Due to the nature of carbon fiber, I would expect the hole to drill a bit smaller than the bit due to spring back.

    That being said, I would try a #18 or a 11/64 drill bit. Both are pretty close. Then there is the problem of actually measuring the hole once it's drilled. Do you have a Go/NoGo gauge set or pin gauges to measure the hole?

    I think some experimenting is in order.

    I don't think you have a chance of trying to grind the drill bit.

    Jim Dawson
    Sandy, Oregon, USA


  3. #3
    Member
    Join Date
    Aug 2015
    Posts
    86
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    +\- 0.0004 is a lot to ask from a drill bit.

    I can't find a drill bit in that range of specifications. The best I can find is a .1705 reamer. MSC part # 03371234, M.A. Ford, carbide.

    Best of Luck.



  4. #4
    Member
    Join Date
    Nov 2017
    Location
    United States
    Posts
    399
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by Jim Dawson View Post
    First I think I would go back to the engineer and have a chat, maybe a more standard size would work. It seems a bit strange that the spec would be an odd size.

    The odds of a hole being drilled exactly to the bit size is small at best, drilling is a roughing operation. Due to the nature of carbon fiber, I would expect the hole to drill a bit smaller than the bit due to spring back.

    That being said, I would try a #18 or a 11/64 drill bit. Both are pretty close. Then there is the problem of actually measuring the hole once it's drilled. Do you have a Go/NoGo gauge set or pin gauges to measure the hole?

    I think some experimenting is in order.

    I don't think you have a chance of trying to grind the drill bit.
    So far the other size drills I've used have given a dead on hole size in the cf. Remember, these are only 10mm long flute carbide drills. Only slightly more than a half inch sticking out of the spindle, so its not your average wobbly drilling op that has a general lack of precision. These tiny carbide drills hit pretty much dead on location and size in the cf plate.

    I've already talked to the designer about it. They are using a press in flanged threaded insert that is actually designed for sheet metal. Probably not the best engineering choice, but that's what I have to deal with. He said at 4.3mm the insert will start delaminating the cf when pressing in, and at 4.36mm it will be loose and fall out. So I guess +/- .01mm is a bit overstating. +/-.02 would be The max. The flange on the insert is what takes the actual load, the press fit is just so the insert stays in until the customer assembles the frame.

    So keeping in mind that these drills are extremely short and rigid, would it really be impossible to grind about a thou off it? It isn't the end of the world if I need to order a 25 dollar drill, I just don't know if hss will stay sharp enough for 150 holes in cf. As it is, I already swap out the carbide ones every 200 holes or so to keep them from fraying the cf since they're only 1.78 a peice



  5. #5
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    33766
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    How about a #18, 4.305mm?

    $18 at McMaster Carr, so probably can be found even cheaper.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  6. #6
    Member
    Join Date
    Nov 2017
    Location
    United States
    Posts
    399
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by ger21 View Post
    How about a #18, 4.305mm?

    $18 at McMaster Carr, so probably can be found even cheaper.
    Yeah, that's the lower size I could find. He said at 4.3 it will be too tight and delaminate the cf when pressing in.



  7. #7
    Member Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    3419
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    Maybe the designer should be introduced to LocTite products or cyanoacrylate adhesives

    At <$2.00 each grinding would be worth a try I guess.

    Jim Dawson
    Sandy, Oregon, USA


  8. #8
    Member
    Join Date
    Nov 2017
    Location
    United States
    Posts
    399
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by Jim Dawson View Post
    Maybe the designer should be introduced to LocTite products or cyanoacrylate adhesives

    At <$2.00 each grinding would be worth a try I guess.
    Yeah, for prototyping he may just have to put some ca on them unless he wants to pay more for a special tool. Thing is, this insert is already used on many other models they already have. Large production runs are done in china. I assume it's mostly waterjet, but they must have a 4.33mm drill for the holes. I just do the quick turn around small batches.

    I ordered a couple 4.305 and 4.365. I'll probably drill with the 4.305 and then chase with the ground down bit if I can get that to work. I also ordered a 4.33 gauge pin. Who knows, maybe I can grind some flutes into that and use it to ream/form the 4.305 hole to 4.33. Only needs to get a thou bigger. Probably not even that much. Maybe I can tap some runout into the 4.305 to gain a little lol. Or just use one of my old cheap er collets. Probably already has a thou of runout



  9. #9
    Member handlewanker's Avatar
    Join Date
    Sep 2006
    Location
    Australia
    Posts
    6252
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    Hi, at 4mm + you could get a masonry drill and use a diamond lap to wear it down to size.
    Ian.



  10. #10
    Member
    Join Date
    Nov 2017
    Location
    United States
    Posts
    399
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by handlewanker View Post
    Hi, at 4mm + you could get a masonry drill and use a diamond lap to wear it down to size.
    Ian.
    Whatever I do, it has to be quick and efficient. The ones I already did, I just interpolated with my 2mm cutter. It works, but it takes extra time to dial it in and also have to recheck every 50 holes or so since the tools wear very fast on cf and diameter of tool can easily go down .01mm in 50 holes. Getting them round is also a challenge when interpolating with a 2mm cutter because of flex and the fact that radial tool engagement changes as it starts and moves through the cut. I have to do spring pass to help with that, which makes the wear problem even worse.

    I'm glad I didn't waste 25 bucks on a hss 4.33mm drill. Last night I did some small m3 countersinks using a 1/4 hss spot drill, tried anyway. It ate the tool in literally 20 countersinks. Hss is definitely a no go for cf, even with very short term usage. Had to finish the countersinks by interpolating with a carbide chamfer. Looks like the only reliable efficient way to do these holes is with a carbide 4.33 drill. Really hoping I'll be able to grind down the 4.365 bits. If not, I'll just have to keep dealing with the pain of interpolating. My new cutters i have coming should at least help with that



  11. #11
    Member
    Join Date
    Aug 2004
    Location
    spain
    Posts
    696
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    I suspect what you want is a carbide reamer.

    Since you seem happy with interpolated holes, I also suspect you don´t achieve 0.01 mm +/- in size cylindricity and straightness.
    Do you have go / no go gages of 0.01 mm size difference to qualify size and straighness of the holes ?

    No Q. intepolated holes can do 0.01 mm, but on high end machines with industrial tooling.



  12. #12
    Member handlewanker's Avatar
    Join Date
    Sep 2006
    Location
    Australia
    Posts
    6252
    Downloads
    0
    Uploads
    0

    Default Re: Slightly sizing down a carbide drill

    Hi, now if you had a Deckle SO D bit grinder you could take a long round carbide blank and grind it to a hex shape for 10mm or so......you drill first with a normal drill and use the ground drill to take out the last couple of thou…….the hex shape will cut just as good as a real reamer but you can custom grind it to whatever size you need.....the hex shape or even a square one automatically has clearance behind the cutting edge......a hex one just has more edges.

    The other dodge would be to use a boring head with a single flute carbide end mill.
    Ian.



Page 1 of 2 12 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Slightly sizing down a carbide drill

Slightly sizing down a carbide drill