# Removing stripped grub screw?



## lazylathe (Jul 19, 2011)

Hi All,

I recently bought a second hand Pm Research Model 3A in fairly good condition.
A bit of rust here and there and a few things to fix.
This is the engine:
http://www.pmresearchinc.com/store/product.php?productid=3086&cat=4&page=1

When i received it the inlet pipe was snapped off in the cylinder and i need to remove the bit left inside.
Any ideas on how to do this?

Also the main problem is the flywheel grub screw is stripped.
I have the correct size allen key for it but it just spins inside the head.
What options do i have for removing it?
I was thinking of drilling it out and retapping for a bigger size grub screw as my only option.

Any help or advice appreciated!

Andrew

Ps - on reading the PM research description of the engine now available i see that the one i have is quite old!
There are no aluminium castings on mine, they are all cast iron and bronze.
A very heavy model!


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## maverick (Jul 19, 2011)

You may be able to use a left hand drill bit a little smaller than tap drill size. Clamp the flywheel in your 
mill vise and align the set screw with the drill. Remember to run the drill the correct direction and gently start 
drilling. When you have got the drill point cutting give the quill handel a series of short increases in pressure.
This will cause it to take a thicker chip and often back the screw right out of the hole. When it works it looks
like magic, if not you have to drill it anyway. Best of luck with your repair.

Regards,
Mike


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## jonesie (Jul 19, 2011)

hi andrew . on the inlet pipe you could try and use a small easy out which is inserted in the end , it has a left hand sprial and will tighten itself in the hole and then just turn it out. on the grub screw you can hold the flywheel tight in a vise with the screw up and pick up as close, to center as possible, then drill it out with the correct tap size drill or try a smaller hole to start and if you have a small enough easy out do the same as for the inlet pipe, but the screw is pretty small, so drill it with the tap drill and then try to retap, stop the drill short of going to deep in shaft but enough to let you retap, the little bit of screw should back out . before doing this apply some pb blaster or other penatrating oil and let it sit for a while just go slow and take you time and make sure you are real close to center. good luck jonesie


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## Ken I (Jul 19, 2011)

Andrew, I have a selction of home made Allen Keys made deliberately oversize and tapered specifically for extracting "burst" / stuck grubscrews.

http://www.homemodelenginemachinist.com/index.php?topic=11370.msg124326#msg124326







For a busted pipe / nipple try an Allen key that will "broach" its 6 corners into the bore of the "pipe" - sharpen the face of the Allen key. (Cut a straight piece of Allen key shank - turn or grind a pilot onto it - as well as sharpen up the corners - and drive it into the pipe with a hammer - remove with a spanner or hex socket.
Obviously do all the other good things like applying penetrating oil, heating, gentle persuasion with a punch & hammer etc.

An Easy-Out will not work if its stuck (if the parent material wouldn't extract it - then neither will and Easy-Out) - they'll work only on something that broke but is otherwise not badly stuck.

Ken


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## rkepler (Jul 19, 2011)

For both of those jobs I use the square extractors from Proto. Here's a link:

http://www.stanleyproto.com/default.asp?CATEGORY=BH_EXTRACTOR&TYPE=PRODUCT&PARTNUMBER=DT-55

They have a square section and are tapered, so for a setscrew I grind the face down until it's about right, then press it into the remaining hole while turning it to engage the setscrew. The flutes usually grab and the screw comes out. I like the square section better than the high helix Ez-outs because the latter can wedge the screw into the hole, the square ones don't seem to do that.


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## Stan (Jul 19, 2011)

I have no knowledge on 'old' PM Research models but if the grub screw has an allen head then it is likely too hard to drill with small HSS bits. I assume that the flywheel is on the engine so it will be difficult to set it up on a drill press or mill table with a drill bit that is longer than the radius of the flywheel.

If none of the suggested methods work to remove the screw I would resort to a diamond point fastened into a shaft extension on a Dremel tool, and grind it out. Diamond points are cheap from places like Harbor Freight

http://www.harborfreight.com/catalogsearch/result?q=diamond+points

When you are faced with sacrificing either the flywheel or the crankshaft, you can spend a lot of time on careful work to save them.


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## mklotz (Jul 19, 2011)

Add my vote for a slightly oversize Allen wrench ground down at an angle and wedged/hammered into the grub screw hex hole. A similar device for the pipe would be what I would try first.


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## GailInNM (Jul 19, 2011)

Sometimes a narrow piece of thin (0.002inch or so) brass shim can be inserted in the screw socket and then the hex driver hammered/pressed into the hole. Think of a width about the width of one side of the hex. 

Someone once told me that a piece of small diameter copper magnet wire would work the same way but I have not tried that.

Gail in NM


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## Catminer (Jul 19, 2011)

Andrew

Before trying any thing that involves hammering or tapping on the setscrew, follow Mikes idea of the flywheel in a vise or support the flywheel in some way. Before trying to move the grubscrew find or grind a pin punch that will go inside the socket of the screw. A couple of sharp blows should loosen the screw from its set on the shaft. This of course will make the indent in the shaft a little deeper requiring more force to remove the flywheel. Maybe a metric hex key might be close in the rounded hole or as suggested a key modified to fit. Usually SHSS are not that hard to drill with a good hss bit, but go slow it will work harden.

Peter


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## Antman (Jul 19, 2011)

Hi Guys,
 I need to do some work on my shaper but the big shop-made 100t rachet wheel is locked on to the leadscrew by a grub screw through an integral collar. I guess I'll have to use something like Marv's method ... one day.
  Ant


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## doubleboost (Jul 19, 2011)

Rounded off cap heads are a common problem at work
I use spline drive bits that are a good hammer in fit
The hyammering in helps to loosen them as well


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## lazylathe (Jul 19, 2011)

Thanks for all the help!!!

I managed to loosen it slightly and slide the flywheel off.
Now i still need to try and remove the grubscrew...

I will let it soak in penetrating oil for a while more and add some heat and see what happens.
Will try and use a small bit of copper and hammer the allen key in and try and loosen it that way.

Andrew


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## ShedBoy (Jul 19, 2011)

One trick I have used is to build up some bronze welding on the end of a scacrificial allen key and while it is still hot hammer it into the hole and let it cool down in place. It makes the size key you need even if odd shape and gets localised heat into the screw. I got this idea from a CV joint repair man, there is a breed of car which has the joint held onto a spline shaft with a hidden clip you can pull the joint off the shaft easy enough but it snaps the last part of the spline off. To save the cost of buying a new shaft he puts on an old joint centre, build up the broken spline with bronze then when it is cooling down he hit the centre off and it leaves a new set of spline. He takes about 5 minutes to do the whole job and says he has been doing it for years and never had one fail.
Brock


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## MachineTom (Jul 19, 2011)

First don't crank up the drill. Take a punch, not just a piece of rod but a hardened punch, find or make the end so it just fits inside the hex of the grub screw, solid against the bottom of the hex, support the flywheel against an anvil or large solid block of iron, 2 sharp wacks with a hammer. What you are doing is setting the cup edge of the screw a bit deeper into the shaft, which will reduce the friction on the screw threads, and allow it to be unscrewed. A strip of .002 feeler strip cut the width of the allen hex, laid across the end of the screw, then tap the allen wrench into the grub screw should tighten up the fit of the allen enough to remove it.


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## Stan (Jul 19, 2011)

PM Research catalog says this is a 2 1/4" flywheel so I am guessing a #4 (.050" socket) or a #6 (1/16" socket). Making your own hexagonal tools in these sizes takes a skill level that is certainly beyond me.

Andrew: If you have the flywheel off it might be easier to try and run the screw into the bore where you know the threads are good and then run a tap in to clean the top of the hole. If this is a 4-40 thread it is easy to damage the top threads when using a worn hex key.


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