Drilling heads off grade 8 bolts

m16ty · Feb 16, 2020

We've got a project coming up where we will more than likely have to drill the heads off of some 5/8" Allen head bolts.

We've done this project before and know a little about what we are getting into. We are removing aluminum plates from a huge gantry mill (16' X 100' bed). When installed, the procedure is to bolt the aluminum plates down with 5/8" Allen bolts, put in a aluminum plug with putty on top of that, and then epoxy to surface. The problem is, they were sloppy with the installation, and didn't seal the bolt off good with plug and putty, and the epoxy ran down on the bolt on some of the bolts.

Like I said, we've don't this before, and fought the epoxied bolts, and they are almost impossible to get out. The last time we used heat that worked on some to soften the epoxy, but didn't work on all of them. We ended up torching the heads on some, but that was a real pain. We even hand drilled some out, but that didn't work well either.

What I'm looking at doing is getting a big steel plate for a base (because the plates are aluminum) and using a mag-drill to drill the heads off of the bolts. What I'm needing to know is what is the best drill bit to drill the heads off of grade 8 Allen bolts.

thermite · Feb 16, 2020

m16ty said:
We've got a project coming up where we will more than likely have to drill the heads off of some 5/8" Allen head bolts.

We've done this project before and know a little about what we are getting into. We are removing aluminum plates from a huge gantry mill (16' X 100' bed). When installed, the procedure is to bolt the aluminum plates down with 5/8" Allen bolts, put in a aluminum plug with putty on top of that, and then epoxy to surface. The problem is, they were sloppy with the installation, and didn't seal the bolt off good with plug and putty, and the epoxy ran down on the bolt on some of the bolts.

Like I said, we've don't this before, and fought the epoxied bolts, and they are almost impossible to get out. The last time we used heat that worked on some to soften the epoxy, but didn't work on all of them. We ended up torching the heads on some, but that was a real pain. We even hand drilled some out, but that didn't work well either.

What I'm looking at doing is getting a big steel plate for a base (because the plates are aluminum) and using a mag-drill to drill the heads off of the bolts. What I'm needing to know is what is the best drill bit to drill the heads off of grade 8 Allen bolts.

The best "drill" for that is probably NOT a drill. Hitting the Allen socket can f**k it up.

"Plunge" end-mill that takes-down the face without dipping into the hex cavity, rather. Another possibility is a small-enough annular cutter. Great friends of mag drills, already, annulars be. Carbide might be best for either?

Put a hardened drill-bushing into that steel plate you are fabbing so you can guide without a pilot, drill the plate for edge pins, angles, clamps, cross-hairs or similarly easy alignment to the target f**kedbolt and solid grip to the beam.

"Mag" ain't the only solution. Or need not work unaided. Yah can also BOLT a drilling head in place, ELSE bolster-guide and add fixed clamp-down to a common maggie. Rented, even, if yah don't ordinarily keep a "right sized" one around.

IOW, treat it as proper production fixturing you can handle safely, line-up accurately and easily, clamp with trust and confidence, not "just" a redneck band-aid for a pain in the anatomy.

What you invest in a better fixture pays back on faster, easier holes with lower risk of f**k-ups or injury.

Bill D · Feb 16, 2020

Carbide endcutting endmills would be my first choice from my limited experience. Is there any solvent for cured epoxy? How about acid or alum to corrode the steel. A tap destroyer would work well here.
Bil lD

m16ty · Feb 16, 2020

I had thought about a end cutting end mill, and we may try that. We don't have to be super precise, as the aluminum plates are scrap, we just need to be lined up close enough to remove the head. Ideally, we would have a cutter the same size as the counter-bore in the plate, and just use that as alignment. If we get lucky, we wont run into any epoxied bolts, but experience tells me otherwise. It's a quote job, with a clause that states any epoxied bolts could incur extra charges.

What they are, are big aluminum vacuum plates, and are sacrificial. Seeing as how the mill is so long, they have to do a surface cut about once a month, to keep the bed in alignment with the cutting head. These mills we are working on were a design flaw from the beginning, and after being milled down and gotten thinner, the plates are giving more problems. The problem is that the aluminum plate joints align with the mill bed joints. This has always caused they joints on the plates to move, requiring more frequent milling to remain within spec. We are removing to old plates, and installing new plates that split the bed joints.

They can use the mill itself to drill out the surface epoxy, but have to stop at the bolt head. They claim the mill heads don't have enough torque to drill the bolts (setup for milling aluminum).

thermite · Feb 16, 2020

m16ty said:
I had thought about a end cutting end mill, and we may try that. We don't have to be super precise, as the aluminum plates are scrap, we just need to be lined up close enough to remove the head. Ideally, we would have a cutter the same size as the counter-bore in the plate, and just use that as alignment. If we get lucky, we wont run into any epoxied bolts, but experience tells me otherwise. It's a quote job, with a clause that states any epoxied bolts could incur extra charges.

What they are, are big aluminum vacuum plates, and are sacrificial. Seeing as how the mill is so long, they have to do a surface cut about once a month, to keep the bed in alignment with the cutting head. These mills we are working on were a design flaw from the beginning, and after being milled down and gotten thinner, the plates are giving more problems. The problem is that the aluminum plate joints align with the mill bed joints. This has always caused they joints on the plates to move, requiring more frequent milling to remain within spec. We are removing to old plates, and installing new plates that split the bed joints.

They can use the mill itself to drill out the surface epoxy, but have to stop at the bolt head. They claim the mill heads don't have enough torque to drill the bolts (setup for milling aluminum).

That's simple ignorance. Or stubborness as to not wanting to switch endmills, RPM, and feed.

Millhand decides what work a mill will do. Only vote a mill gets off its limitations is "how soon DONE"?

One could start-off with with tooling that handles BOTH shiney-wood and real-steel, change speed and feed only when they hit the bolt's head depth.

And if the PLATEs are to be SCRAPPED? Might want to just go at it with a LARGE annular, leave the bolts as "islands" to be wrenched-out.

Not only is positioning now less critical, you can be well-enough assured to give the steel grade 8's a full MISS 'til you can crank 'em out by gripping their "mushroom head" surviving disk, epoxy, plug, wotever - its free of the plate and "fair game".

Demon69 · Feb 17, 2020

Rather than trying to drill the entire head off, maybe you could use the max size drill that'll fit into the head of the bolt and drill deep enough to get past the head. A thump with hammer/chisel should finish of the job.
Grade 8 shouldn't be too bad, I thought most cap head bolts were tougher than that tho.
GL

muckalee · Feb 17, 2020

Socket head cap screws are not grade 8 bolts. The head of a shcs is work hardened by the forming process and can be difficult to cut. If the cavity of the head is filled with epoxy, drill out the epoxy with a drill bit 0.375 diameter or smaller and use a cape chisel to remove the epoxy from the corners of the head cavity. Most any pointed chisel should also remove the epoxy. A cordless drill, chisel and small hammer.

cyanidekid · Feb 17, 2020

Demon73 said:
Rather than trying to drill the entire head off, maybe you could use the max size drill that'll fit into the head of the bolt and drill deep enough to get past the head. A thump with hammer/chisel should finish of the job.
Grade 8 shouldn't be too bad, I thought most cap head bolts were tougher than that tho.
GL

Yea, demon is on to something there!
But as to hardness, Not necessarily. “grade 8” is a garbage grade anyway for the most part, Just putting 6 hashes on a bolt head doesn’t mean anything. Hardness is just one factor in a fastener as well, and not a good thing at all in and of its self. So much BS on fasteners..

Standard Pressed Steel UNBRAKO was the gold standard, what are they, 180k psi? But most are more akin to 150? Still should be drillable with cobalt HSS.

It’s on a freakin mill and the dipshit says “it can’t be milled” what the hell? You can get up on that with a cordless drill and be done with it.

thermite · Feb 17, 2020

muckalee said:
Socket head cap screws are not grade 8 bolts. The head of a shcs is work hardened by the forming process and can be difficult to cut. If the cavity of the head is filled with epoxy, drill out the epoxy with a drill bit 0.375 diameter or smaller and use a cape chisel to remove the epoxy from the corners of the head cavity. Most any pointed chisel should also remove the epoxy. A cordless drill, chisel and small hammer.

So now a tedious and labour-intensive process has completed, an Allen-key can be inserted, the bolt circumference, underhead, and even shank may still - from experience - be epoxied in place.

And we are going to go this extra mile so an already known-scrap plate is less ugly?

Annular cutter.

"Trepan" around them.

Plate is now asided.

Apply Stilson wrench to twist the protuding buggers - now standing tall in open air - right TF out.

Take the core slug of scrap shiney-wood WITH them if it has been epoxied to any given fastener.

EmGo · Feb 17, 2020

m16ty said:
They can use the mill itself to drill out the surface epoxy, but have to stop at the bolt head. They claim the mill heads don't have enough torque to drill the bolts (setup for milling aluminum).

How fast will the spindle turn ? How about using an abrasive, like a 1" cbn grinding wheel ? Then you could even program the head to do the job, controlled feed and tight position holding and all that.

Bondo · Feb 17, 2020

If you dont want to use a torch or carbon arc, then my choice would be to use a large annular cutter to cut a bore out and then go after the bolt.

If possible, can you fill the bolt head with sand before epoxy. Would that help keep most epoxy out of the bolt head?

Sent from my SM-G960U using Tapatalk

Limy Sami · Feb 17, 2020

According to the charts I've seen 5/8 allen heads are <> 15/16 / 24mm dia, so how about an M42 HSS Rotabroach cutter, and drill the outside of the head away leaving the (possibly) work hardened hex hole
5/8 bolts use a 1/2 key which should measure <> 0.577 across corners ..so as long as the bore of the Rotabroach is under 5/8 - jobs a goodun

P.S. I said M42 HSS for resistance to chipping (which carbide is very prone to) and run it SLOW SLOW

ON edit Bondo beat me to it.

DDoug · Feb 17, 2020

Why the mag drill ?
Can't you program the gantry mill to doo the work ?

Scottl · Feb 17, 2020

Bill D said:
Carbide endcutting endmills would be my first choice from my limited experience. Is there any solvent for cured epoxy? How about acid or alum to corrode the steel. A tap destroyer would work well here.
Bil lD

There used to be a solvent sold for cured epoxy but for some reason (environmental or user safety?) it is no longer on the market. It might sound weird but I'd be tempted to try something like Trizol Creep with the heat. It might just get between the epoxy and metal enough to get the bolts out. I've never tried that but I've used it with a torch to get a cast iron cleanout plug out of a cast iron soil pipe without having to break the plug. The plug had been in for at least 50 years.

gbent · Feb 17, 2020

My thought is to drill out the epoxy with a 1/2" bit and hand drill. Sharpen the end of a 1/2" hex driver so the corners are dead square. Hammer the hex driver in the hole, it will shear the remaining epoxy out of the corners. You may have to remove the hex driver a couple of times and redrill the socket. Remove the shcs with a rattle wrench, you need the impacts to break loose the epoxy.

Archer120x · Feb 17, 2020

One more option is to weld nuts to the top of the screw. They will come out easy then. The heat really loosens things up.

atex57 · Feb 17, 2020

My first stop would be an air hammer with a blunt point to fit into the socket. The beating of the hammer would knock out the epoxy and shake the screw to loosen it. Done it many times on old rusty stuff.

Ed.

Guest · Feb 17, 2020

m16ty said:
They can use the mill itself to drill out the surface epoxy, but have to stop at the bolt head. They claim the mill heads don't have enough torque to drill the bolts (setup for milling aluminum).

What? So you are telling me a huge gantry mill big enough to park a half dozen full sized SUVs end to end on the bed doesn't have a head on it with enough torque to drill out a 5/8" bolt? I could do that on a 2HP manual mill.

WizardOfBoz · Feb 17, 2020

Scottl said:
There used to be a solvent sold for cured epoxy but for some reason (environmental or user safety?) it is no longer on the market. It might sound weird but I'd be tempted to try something like Trizol Creep with the heat. It might just get between the epoxy and metal enough to get the bolts out. I've never tried that but I've used it with a torch to get a cast iron cleanout plug out of a cast iron soil pipe without having to break the plug. The plug had been in for at least 50 years.

Epoxy is a thermoset, meaning when it cures, the small epoxy molecules react to cross link together. So a chunk of cured epoxy is essentially one big molecule. It cannot dissolve, and to get it into solution you'd have to chemically cut those bonds. That would take some nasty actors.

If you look at a chemical resistance chart for epoxy, it rates "Good" or "Excellent" for pretty damn near everything. Except for acetone and some pretty nasty actors like fluorine gas and hydrobromic acid. If you want to dig epoxy out, you'd need to soak it for a while in acetone and hit it with heat (careful wiht the combo of heat and volatile solvent!). The suggestion thermite and others made seams best. Use the mill to drive annular cutters to remove the plates. At that point you can put a big old pipe wrench* on the nipple that remains.

*You can use a Stillson pattern pipe wrench if you want...

akajun · Feb 17, 2020

Archer120x said:
One more option is to weld nuts to the top of the screw. They will come out easy then. The heat really loosens things up.

That's what I was thinking, pre heat with a torch, wire brush the burned epoxy off, mig on an old nut and hit it with an impact gun.

Drilling heads off grade 8 bolts

Hot Rolled

Diamond

Diamond

Hot Rolled

Diamond

Titanium

Cast Iron

Titanium

Diamond

Diamond

Hot Rolled

Diamond

Diamond

Diamond

Diamond

Cast Iron

Stainless

Guest

Guest

Diamond

Stainless

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