Belly Tank Build Diary

[Mike Brown]

A photo of drilling the 1/16" hole in a bolt.  The flat was milled before this photo. 

[tauruck]

Mike, that's some awesome advice. I was scratching my head about doing that very job.
You just saved me a large head ache. Thanks. Regards, Mike.

[fordboy628]

I like to use safety wire on critical fasteners used in assemblies like suspension.  I am adverse to drilling 1/16" holes 1-1/8" deep through the heads of grade 8 bolts.  I prefer to drill through the corner of the hex.  This same methodology can be used for nuts. I purchased a drill jig for this purpose but was not satisfied with the results. I broke too many drill bits ruining expensive bolts.  I came up with a successful methodology using my milling machine.  I find the edge of the hex point and move into the bolt 1/8".  I mill a flat using a solid carbide two flute Kennametal end mill which makes a flat.  I then step back another .020" and drill a 1/16" hole using a Guhring parabolic flute drill bit.  I have drilled over two dozen holes without breaking a bit.  I keep the speed down to 1,500 rpm and use synthetic gear oil to lubricate both the end mill and drill bit.  

The aluminum jigs sold for this purpose are JUNK, do not waste your money on them.    I have and use a WWII era surplus jig, made of tool steel, for this purpose.

The aluminum jigs allow the drill to "wander", enlarging the jig hole in the fixture.    Drill breakage starts immediately thereafter.     Also, "low twist" (helix) cobalt drills with 135 degree point angle work best for me.   I could probably make a 118 degree, regular twist drill bit work in a pinch, but DO NOT use high helix drills, as they are very "flexible".   High drill bit rpm, light feed rate and cutting fluid definitely help drill bit life and reduce drill bit breakage.    Instead of the end mill trick to start, a small diameter center drill can be used.   Again cobalt, high rpm, low feed and cutting fluid are required.

If you are drilling a LOT of Gr8 or hardened "Allen head" bolts, find or machine a tool steel fixture, and get the cobalt drills.    You will save your sanity in the long run.

Just my 2¢


Fordboy

[Mike Brown]

I like to use safety wire on critical fasteners used in assemblies like suspension.  I am adverse to drilling 1/16" holes 1-1/8" deep through the heads of grade 8 bolts.  I prefer to drill through the corner of the hex.  This same methodology can be used for nuts. I purchased a drill jig for this purpose but was not satisfied with the results. I broke too many drill bits ruining expensive bolts.  I came up with a successful methodology using my milling machine.  I find the edge of the hex point and move into the bolt 1/8".  I mill a flat using a solid carbide two flute Kennametal end mill which makes a flat.  I then step back another .020" and drill a 1/16" hole using a Guhring parabolic flute drill bit.  I have drilled over two dozen holes without breaking a bit.  I keep the speed down to 1,500 rpm and use synthetic gear oil to lubricate both the end mill and drill bit.  

The aluminum jigs sold for this purpose are JUNK, do not waste your money on them.    I have and use a WWII era surplus jig, made of tool steel, for this purpose.

The aluminum jigs allow the drill to "wander", enlarging the jig hole in the fixture.    Drill breakage starts immediately thereafter.     Also, "low twist" (helix) cobalt drills with 135 degree point angle work best for me.   I could probably make a 118 degree, regular twist drill bit work in a pinch, but DO NOT use high helix drills, as they are very "flexible".   High drill bit rpm, light feed rate and cutting fluid definitely help drill bit life and reduce drill bit breakage.    Instead of the end mill trick to start, a small diameter center drill can be used.   Again cobalt, high rpm, low feed and cutting fluid are required.

If you are drilling a LOT of Gr8 or hardened "Allen head" bolts, find or machine a tool steel fixture, and get the cobalt drills.    You will save your sanity in the long run.

Just my 2¢


Fordboy

The fixture that I purchased was hardened tool steel with a jack bolt to keep the corner of the hex pressed tightly against the fixture.  The problem that I had was pulling these stringy hard chips all the way up through the fixture without the chips binding the bit.  With no fixture and the parabolic flute bits pulling these chips up to just clear the drilled hole is no problem. 

[Rex Schimmer]

Mike,
I like your lock wire hole drilling method however because for years I did not have a mill I would clamp the bolt in the drill vice with one flat perpendicular to the drill head and then near the edge of the hex I would drill a shallow hole with the 1/16 drill then I would turn the bolt so that the shallow hole was now on the side and very carefully insert the drill, while turning, into the shallow "pilot" hole which is now at approx 60 degrees from vertical, and start drilling slowly. If I took my time and used good drills I was pretty successful. Much easier on a mill. Lots of ways to skin the cat!

Rex

[manta22]

That's the way I've done it too, Rex.

Regards, Neil  Tucson, AZ

[Peter Jack]

That's the method I've always used with great success. Thanks Rex. While I was figuring out how I was going to photograph the operation you made a totally clear picture using only words. Well done!  

Pecking at the hole in short bursts rather than using steady pressure seems to help by keeping the hole clear and the drill bit cool.

Pete

[Mike Brown]

The benefit of using a parabolic flute drill bit is that you don't have to "peck" drill the hole to clear the chips.  With a standard flute drill bit you should be able to drill holes 3 times the bit diameter without the need to peck or clear chips.  Depending upon the parabolic flute bit holes can be drilled 5 or 10 times the diameter because they "pull" the chips out of the drilled hole.  When chips pack in the hole there is a lot of sliding going on which greatly increases the heat and the chance of catching which causes bits to break.  With some materials like stainless steel the heat will quickly work harden the material.  When the chip comes out cleanly the heat of the cutting action comes out with the chip.  I was able to drill the 1/16" holes without pecking.  I attached a photo of a drill chip that is almost an inch long attesting the to fact that the parabolic flute bits do a great job with these hard stringy materials. 

[Rex Schimmer]

As I am a real "tool junky" I guess I need to be getting some of the parabolic flute drills and give them a try.

Rex

[fordboy628]

Are "parabolic flute" drill bits the same as, or similar to, "high helix"?

[NathanStewart]

I think I read that this is an ECTA car only but I believe they more or less follow the SCTA rule book.  There's one paragraph from one rule that many, many special construction racers miss.  Last paragraph of rule 3.D.3 Arm/Leg Restraints: "All Special Construction vehicles shall included an inner liner or system of roll cage members for driver protection in the event of body panel destruction or separation.  For a restraint system to be deemed acceptable, no part of the driver shall extend outside the inner plane of the roll cage structure".  That means plate on the outside of the cage is not acceptable.  Just sayin'.

[Mike Brown]

Are "parabolic flute" drill bits the same as, or similar to, "high helix"?

A parabolic flute drill bit may be high helix but it actually refers to the flutes of the bit which are shaped to pull the chips up from deep holes.  They can be had in high speed steel, cobalt, carbide and with various point angles.  I like Guhring brand.   

[ronnieroadster]

I think I read that this is an ECTA car only but I believe they more or less follow the SCTA rule book.  There's one paragraph from one rule that many, many special construction racers miss.  Last paragraph of rule 3.D.3 Arm/Leg Restraints: "All Special Construction vehicles shall included an inner liner or system of roll cage members for driver protection in the event of body panel destruction or separation.  For a restraint system to be deemed acceptable, no part of the driver shall extend outside the inner plane of the roll cage structure".  That means plate on the outside of the cage is not acceptable.  Just sayin'.

  Natan you have a great eye for the details the ECTA rule is identical to the SCTA rule the inner panels must be on the inner plane of the roll cage an easy correction to do now.
Ron

[fordboy628]

Are "parabolic flute" drill bits the same as, or similar to, "high helix"?

A parabolic flute drill bit may be high helix but it actually refers to the flutes of the bit which are shaped to pull the chips up from deep holes.  They can be had in high speed steel, cobalt, carbide and with various point angles.  I like Guhring brand.   

Thanks.    I can see where the "thicker" core of the parabolic flute would also be "stronger" and more resistant to bending in service.

Checking through my woodworking toolbox, I noticed that the specialty, German made drills I bought for deep hole drilling in wood and acrylic are a parabolic flute design, for "deep hole chip removal".

[Mike Brown]

I fabricated the foot box from 11 gauge steel.  I made a few practice pieces from aluminum before the final version in steel.  The bends were made on a D&K power leaf brake.