damaged allen screws removal

Good morning all.

While restoring a small 8 inch wood surface planer, I have found it difficult to remove two of the grubscrews retaining the blades.

There are two blades with four screws in each. I have managed to remove six of them but the last two have resisted all efforts. I tried heating, wd40, diesel, all to no effect, then tried drilling, big mistake !

AT this stage, I have run out of ideas, but since the rest of the machine is in fairly good condition, I dont want to scrap it.

Any ideas how to get these screws out ? They are sunk well below the surface of the block, needless to say.

How big is the part in which they are stuck?

Clamp it to a milling machine table and have at them with a carbide end mill and high speed.

If you have removed some of them, you will know the thread size and hence the tapping drill size.

Mill/drill them to no more than that size. The two axes of movement the mill offers will allow you to centralise the hole fairly well. If the mill you are using is smaller than the tapping drill size, once the central portion of the screw is removed, you can move a little back and forth and left and right until only a thin shell of screw remains, which can be picked out with a pointy object.

If you cannot bring the part to the machine, make up a drill bushing that can be fixed centrally over the hole and use a carbide mill in an electric drill.

I guess it depends on the size and whether you can get the block out of the machine.

I've had success using a high speed bench drill with solid carbide PCB type drill bits.

Bill

Larry sounds like you have exhausted all the options, however drilling out should work OK but you will have to remove the rotor block and mount in a vice on your mill or drill. Then you can be sure of drilling on centre and true to to the original hole.

Just my thoughts John

Mill/drill off the ‘heads’, as above. Then drill a pilot hole in the remaining shank, followed by larger left-handed drills which will most likely easily remove the remaining threads as the drill size approaches the core size. Careful not to damage the planer blade(s) ax you drill deeper, if it/they is/are otherwise in good condition

Left-handed drills are one of my ‘go to’ options with broken screws/bolts. I never use the common (as in ‘cheap&rsquo ‘easy-outs’ and would certainly not recommend those as an option.

They might be odd sized imperial hex? If so maybe a torx drive might fit? Depends really on how much the grub screws are damaged.

Quick answers indeed !

The block is 55mm dia x 200 long, with no easy way to remove it.

The screws are 6mm grub screws.

It may be possible to remove the tables [more sad screws ? ] and set it up on my mill, should be able to clamp it well enough to try it. If not, I will try plan B.

Thank you both for your ideas.

My first thought would be a spark eroder, assuming normal methods have failed, Drilling with a carbide drill might work but the interupted cut in the hexagon may ruin it. Careful sizing and positioning of the tool will take out the core just leaving the thread as a spring to unwind. The outer thread should be untouched. Good Luck, Noel.

I would carefully drill it and have used LH drills with good results when I did this sort of thing for a living.

Tony

Larry,

Carbide tipped drill will do it. The grub screws tips are probably mushroomed anyway

Well Dave, whatever about the screw tips, the heads are in a sad state !

The other six screws came out clean, with no damage, just the last two.

There seems to be no way to remove the block, so I am devising a way to clamp the machine minus the tables on the mill, while making up a jig to guide a drill or endmill or whatever. I am hoping to use some of the other holes to hold this jig in position.

The other option might be spark eroder, not sure where I can get this done, but will ask around.

The blades are rusted but not gapped as far as I can see [this machine was not too well cared for ], so could be reground or at worse, replaced, they are not too dear anyway.

Sad to see a good machine end up like this.

I am also restoring a 16mm bench drill, and the less said about its condition, the better !

Enough to say that had a few more holes been drilled in the table it might have fallen off !

Whatever you do, do NOT use Easyouts!

Most misnamed tool in the world. More likely to expand the screw into the hole.

I would feel inclided to follow NDIY's advice and try using a Left Hand drill (4 mm would be first try, in case it wanders off centre. Press hard! Hopefully, the torque and localised heat will free the stuck screws. Once they free off a little, they will probably come out fairly easily.

However you go about it, hope that you succeed fairly easily.

keep us posted!

Howard

If these tapped holes are on a tangent then drilling the grubscrews with a hand held pistol drill is not likely to go well as you have discovered.

If the threads are M6 and you have a lathe I suggest making drilling jigs from some M6 bolts by drilling them concentrically (say 4mm) and using them to guide a good quality sharp drill (ideally following the use of a spotting drill) to ensure the best chance of staying on axis. The donor bolts need to be long enough for their hex heads not to collide with the surface of the planer drum

Make several drilling jigs as its likely the bore of the jig will get ovalised.

I have recovered quite a few butchered Allen grub screws using the above method

Ian P

Hammer an allen key into the hole.

Weld it to the screw

Undo with an impact wrench.

Drilling cap head screws is an exercise in desperation

IF the grub screws are good ones (unbrako) then they WILL be very hard ! Any talk of drilling or milling will HAVE to be with carbide or tipped drills. Fine in a pillar drill but hand held, the brittleness of the drill or tip is all to likely to brake the bit or it's cutting edge. Fill hole full of wd40 or similar, hammer on it persistently with an 8Oz hammer using a core size punch. Then hammer in the next size up allen key, pray, then try to undo! Good Luck, you'll need it . Noel.

Are the screw heads just spinning the hex key? I had this happen this week. Got a flat punch the diameter of the head . Belt with a hammer until it flattened the hex section. Then drove the end of a hex key. I needed to cut the bent part of the key off, leaving a long hex section rod. The end of this is what is driven into the flatend section. Then undo with socket on the end of the key.

+1 on Neil's suggestion above. And be sure to use good quality allen keys such as Unbrako. Junk ones round off easily.

Another dodge if the hex hole is still reasonably intact is some coarse valve grinding paste in the hole and on the allen key to give it some grip.

Or sometimes you can hammer an oversized good quality Torx driver into the remains of the hex hole and get a grip that way via its sharp splines.

If you do resort to drilling -- which as said can be tough on high tensile screws -- left hand drill bits that spin in the reverse direction are the best bet. Run very slow in intermittent bursts in a slow but torquey battery drill seems to quite often grab the broken screw and wind it out before needing to fully drill through.

I like Ian,s idea, worth a try.

Nicholas, these screws are buried deep in the block, no way to get to weld anything to them.They are grub screws, not caphead.

Yes the screws are good quality quite hard, as I found when trying to drill them and at this stage the heads are well and truly mashed up .

Another option might be to cut off the screws where they emerge under the blades and drill new holes near the old ones. A thin cutting disc should be able to do the job, crude, I know, but needs must !

I'm not that familiar with how planer blades are held within the rotating drum but if they are just in a slot and its only the pressure from the screw that prevents them being flung out by centrifugal force, then your idea of somehow removing the tip of the screw sounds good.

If there is nothing holding the blade besides the screw pressure (only two remaining now) can you get a wedge or use a screwdriver tip to lever up the the blade in its slot and gradually extract it. The exposed tip of the grubscrews might then be long enough to grip with narrow (or ground down) jaws of Mole type grips. You could then rotate then to screw the grubscrew further into its hole to loosen it and then remove the grubscrew by cutting it off in stages.

The drilling guides I suggested earlier do rely on there being a sufficient length of exposed thread above the butchered screw.

Ian P

If as you say you can cut through the screw between the block and the blade with a slitting disc I would certainly do that. It will at least take the compression off the screw which should leave it under no stress and just threaded into the hole. I would lay odds that unscrewing it would be possible if you can get some kind of grip on the hexagon by hammering an oversized key in.

regards Martin

If it moves you have the option of screwing it further in as well and grinding the next bit off if you haven’t been able to remove the blade by that point.

Edited By Martin Kyte on 26/02/2023 11:13:46

Screw in for preference if the chopped end works, far less to screw in than out.

Regards Ian.