Stubborn locking screw

oldbilbo

oldbilbo

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Help! Practical eng knowhow needed....

I've struggling to disconnect my 1" propshaft from its 'shaft clamp' and that from the flexible coupling. There are four clamp-bolts which have been eased OK using an Allen key. The problem is the locking screw or stud....

This is about 8mm diameter, and there is a 6mm approx. hole down the approximate centre. That hole continues right through the body of the shaft-clamp and well down into the propshaft, but not all the way through. There is a corresponding but empty hole on the other side of the shaft-clamp body but no dimple or penetration on that side of the propshaft.The 'screw' top surface was recessed into its hole perhaps 1mm, and I suspect a previous owner had sheared off the top-slot intended for a screwdriver, then drilled down the centre in a failed attempt to remove it. A colleague considers that it is a roll pin, but there's no sign of concentric/spiral layers.

I'd hoped to drill out most of the remainder of this 'screw', then use a stud extractor on the thin remains, so freeing the shaft. I could then unbolt the shaft-clamp from the flexible coupling, but want/need to remove the 'locking screw' first.

I've tried 2 new left-handed HSS drill bits, one of 6.2mm and one of 7.8mm. These have failed to cut, despite using CT-90 cutting paste, and have merely indented or 'countersunk' a little the top of the screw/stud - as can be seen.

Suggestions are welcomed from better-experienced marine engineers - or anyone else wot knows - on how to remove this stubborn screw/stud. Of course, while I can bring handheld power tools to bear, access is very tight.



IMG_3228.jpg
 
It could be a sheared off S/S screw-they take some drilling. It would be considered poor practice to use a roll pin in such an application-no way to get it out without a bored hole right through. So I suspect it is a S/S screw, sheared off that has been work hardened by previous drilling efforts. Heating cherry red with Oxy Acetylene gear is one way to anneal the metal and thus allow it to be drilled out, but not recommended in confined spaces. If it has been drilled through, down to the shaft, only the small tube of metal will be left. You could try purchasing four longer flange bolts, remove the flange from the gearbox, insert a socket or a nut smaller than the 1 inch shaft and fit the longer bolts to the flanges. You now have an effective press-by tightening the longer bolts evenly the shaft may push out of the clamp. Some scoring of the shaft by the remains of the screw will occur, but easily cleaned up. Good Luck!
 
If it is a rollpin ( and it does look like one ) it would be a pig to drill out.
Have you tried removing the allen bolts completely - half of the coupling should then drop away from shaft. You might then be able to knock the remaining half away from the shaft by tapping the coupling with a hammer.
 
Looks like a slotted spring pin to me. Does the assembly split? Ridiculous to fit such a device in a blind hole.

Best way to remove is to heat the assembly up to cherry red and let it cool slowly. This will anneal the pin allowing it to be drilled easier or if lucky to be pulled out with a decent screw extractor and mole grips.


Edit:

These are NOT decent screw extractors:

5pcsscrewextractorset_208625.jpg
 
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I agree it looks like it could be a roll pin. Can you poke some welding wire down there and see if it is hollow? If the clamp is in two parts, just take all the cap head bolts out, disconnect it from the coupling, and see if the half with the "pin" in it can be pulled off the pin. IF it is NOT in 2 parts and the hole is blind, could you carefully measure the hole position and then drill a hole through the other side until you hit the far side of the pin, then use a pin punch to bash it out the "far" side? I can't see the hole going right through as being in any way injurious to the health of either the shaft or the clamp.
 
stuey_two said:
If it is a rollpin ( and it does look like one ) it would be a pig to drill out.
Have you tried removing the allen bolts completely - half of the coupling should then drop away from shaft. You might then be able to knock the remaining half away from the shaft by tapping the coupling with a hammer.
Click to expand...

If its like the Yanmar clamps that I am familiar with the flanges are not split, only the body where the shaft fits, so it stays in one piece.
 
The 'shaft-clamp-flange' is NOT in two parts, so I cannot separate them to release or gain access to the screw/rollpin. I'd be very reluctant to bring a gas torch/flame to the workpiece, for the risk of burn injury to my face and hands would be high. Access is by 'tight wriggle' and there are numerous plastic, rubber and oily-greasy tubes very close by.

The screw/rollpin is hollow, for I am able to insert the thin steel rod of a cheap plastic caliper gauge down into it. That 'bottoms out' at a depth equivalent to the wall thickness of the flange-clamp PLUS about 15mm, or a little more than half the diameter of the prop shaft. I cannot tell if the screw/pin itself is bottomed into the hole.

There is another hole on the other side of the flange-clamp body, with nothing in it. I guess that I should attempt to drill into the prop shaft from that side, using this hole as a guide, then attempt to punch the thing out as Avocet has suggested.

Would that be best attempted using a cobalt drill bit of nearly the same diameter as the flange-clamp 'guide hole'? And the cutting paste CT-90?
 
Cobalt drill

I don't understand the measurements. If the hole we can see is 6mm dia and you have drilled with a 7.8mm drill, what has caused that big countersink?

That aside I agree with Tranona - clamp the shaft firmly, use a new cobolt drill, plenty of coolant, powerful drill turning slowly, lots of pressure and something will give. You can feel when the drill is cutting rather than rubbing - if not go slower until you can? Use several drills to keep it sharp. Sorry if you know all this already.
 
If that is like Yanmar flanges I have removed, it is a grubscrew.
Or perhaps an ex-grubscrew.

I am surprised the lefthand drills have not done the job.
I think my next skirmish might involve something carbide in a Dremel.
I have a solid carbide burr I use for butchering stainless.
 
Thanks, guys, so far. It's too dark and 'dodgy' to climb up into the boat at present, for severall reasons, so I'll have another 'go' in the morning. And I'll redo the measurements, which I cannot at present.

FYI - and I regret it not coming across unambiguously - the hole in the flange-clamp is 'as best I can measure it' 8mm inside-diameter. Therefore the grub-screw/rollpin thingy stuck in that hole is ~8mm outside-diameter.

Down through the centre of that is a clear hole of 6mm diameter 'as best I can measure it' which extends well into the prop shaft.

The top surface of the grub screw/rollpin thingy, when I'd cleaned away the crud, was flat - but with a vestige of a slot to one side. I thought that looked like the remnants of a screwdriver slot, with the two hemispherical bits broken off. My mate suggested it could be a rollpin, as do others here.

I do have some solid carbide bits, of varying shapes/profiles, but I'm a little hesitant to risk something hard but brittle snapping off in the hole. Perhaps the 'gaining gambit' is to drill through from the other side....

Now, if I can remove this 'grubscrew/rollpin' problem, and unbolt the flange-clamp from the flexible coupling, what will I find inside the bell-end? A keyway and a Woodruff key...? And how might I get that Woodruff key out...?
 
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I would not apply heat as the casting could crack due to uneven expansion
I would get a drill bit the size of the hole in the pin & drill right through the bottom of the blind hole. Then use this as a guide to drill a bigger hole from the other side so you can punch out with a drift from the other side
 
oldbilbo said:
The 'shaft-clamp-flange' is NOT in two parts, so I cannot separate them to release or gain access to the screw/rollpin. I'd be very reluctant to bring a gas torch/flame to the workpiece, for the risk of burn injury to my face and hands would be high. Access is by 'tight wriggle' and there are numerous plastic, rubber and oily-greasy tubes very close by.

The screw/rollpin is hollow, for I am able to insert the thin steel rod of a cheap plastic caliper gauge down into it. That 'bottoms out' at a depth equivalent to the wall thickness of the flange-clamp PLUS about 15mm, or a little more than half the diameter of the prop shaft. I cannot tell if the screw/pin itself is bottomed into the hole.

There is another hole on the other side of the flange-clamp body, with nothing in it. I guess that I should attempt to drill into the prop shaft from that side, using this hole as a guide, then attempt to punch the thing out as Avocet has suggested.

Would that be best attempted using a cobalt drill bit of nearly the same diameter as the flange-clamp 'guide hole'? And the cutting paste CT-90?
Click to expand...

In my humble opinion you would be better served by drilling right through the shaft from the side with the screw, using the existing hole as a guide. USE A GOOD BIT, SLOW SPEED, PLENTY OF LUBE AND LOTS OF PRESSURE. Once through you will have a small hole perfectly in line with the opposite side. This will give you a pilot for a larger drill to go through from the other side to clear the end of the screw or pin.
 
if it were mine I would use an angle grinder to remove the countersink at the top,as it looks shallow , it would then show if it is a roll pin or not.

judicious tapping of the slot might turn the pin if lucky.
 
has the make of the clamp been identified ? If an ID, then perhaps some engineering drawings might be available.
 
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