Grub screw has turned to cheese!

[John CoatesParticipant @johncoates48577]

Screw out but how/where to get replacement

[John CoatesParticipant @johncoates48577]

On my lathe was a non-original cone drive pulley located with a grub screw. Having got a new pulley I went to remove the cone pulley and for some reason, the grub screw was steadfastly stuck and the slot head rapidly turned to cheese. Only a screw extractor got it out!

 

So now I have a cone pulley sans grub screw and a new pulley that won’t go fully onto the motor drive spindle (maybe either the casting or the motor spindle isn’t true). So doing anything on the lathe is out

 

The grub screw is/was a 6.5mm bolt of 1.25mm pitch. This now has a mangled head and a hole part way through it

 

So what are my options? I could try and drill more of a hole in the old grub screw and see if a small allen key would work with it. Or can you buy grub screws from somewhere?

 

If I use the old grub screw it will get well lubricated before it goes back in the hole again!

 

Your help and advice will be well received

 

John

[mgjParticipant @mgj]

Grub screws are cheap as chips and common as dirt. Go to any fastener supplier on any trading estate (yellow pages).

 

You and I call them grubscrews, but they call them something else, but you want the kind with a socket cap, and not a slot head.  Setscrew from memory.

 

If you are putting a grub screw into ali, you might buy a small tube of Copaslip or equivalent. Actually if you are putting a grub screw into anything, some Copaslip is good engineering.

 

Find a thread a smidgen bigger than the one you have taken out, and retap. Or get it helicoiled.

 

If you are really really pressed, let me know, I might JUST, but only just, be able to spare you an 8mm grub screw., so rare are they. 

Edited By meyrick griffith-jones on 24/11/2009 22:17:31

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

The other half of the double act here.

If I might relate a little tale involving a Myford motor pulley, there is a moral if you stick with it I recently had to take the 3 phase motor off my Myford to play with the windings to convert it to 240V so that my new my VFD would work.  Now it is not easy to get at the back to undo the bolts holding the motor on to its bracket, so I could not see clearly what I was doing  (I know ,no change there) anyway Moral 1 if you have a resilient mount motor you only have to undo the  two small screws in the clamps holding the rubbery bits, not the four hard to get at ones, doh.

Next comes removing the two step pulley, normally you just undo the grub screw and hey presto, yeh right. The grub screw is at the back and hard to see, still I tried all suitable IMP Allen keys, yes genuine Allen  Allen keys, but it gave the feeling that the hex was worn out, no grip. What to do? Moral 2, get out the hot air gun and warm the alloy up. Then apply a three jaw puller, not two jaw which is more likely to  snap the alloy. Came off sweet as a sweet thing that comes off easily. Once off, the problem with the grub screw was simply that the hole was stuffed full of rubber, at some stage the belt had run on the boss and shed some of its self, not recommended in Noddy’s book of the Myford.

chriStephens

[CirclipParticipant @circlip]

Hmm, since Mo and Curly have jumped in, here’s Larrys take. 6.5mm X 1.25 P sounds awfull close to 1/4″ X 20 TPI.??

[Ian S CParticipant @iansc]

If your pully is aluminium,Whitworth or UNC are a better thread than metric.Best if 2 grub screws are used about 90deg apart,ideally a key would be the correct thing.The grub screws should either go into dimples in the shaft or flats filed on the shaft.I tighten up then put a punch in the hex hole and give it a tap,then retighten.IAN S C PS grub screws are hardened.

Edited By Ian S C on 25/11/2009 13:13:08

[Gordon WParticipant @gordonw]

I’ll second Circlip on the Imp. thread. Grub screws for max. effect should be as close together as poss. preferably in line, the idea being to get as much shaft in contact with the bore as poss., not being driven by two screw points.

[John CoatesParticipant @johncoates48577]

Posted by Circlip on 25/11/2009 11:40:52:

Hmm, since Mo and Curly have jumped in, here’s Larrys take. 6.5mm X 1.25 P sounds awfull close to 1/4″ X 20 TPI.??

Which given the fact it is a 1947 lathe is probably the case although the cone pulley must have been a “modification” by a previous owner

 

I have yet to get a BSF Whitworth screw pitch gauge – its on the Xmas present list!

[mgjParticipant @mgj]

Well its 49 thou, so yes its a 20tpi thread.

[TerrydParticipant @terryd72465]

Just a couple of points,  Grub screws are indeed available from local fastener or engineering suppliers and are in fact called ‘grub screws’.  I buy them for projects from a small company locally and they are as cheap as chips.  Set screws are are not another name for grub screws but simply bolts, such as hex head which are threaded all the way up to the head, rather than a short thread on a longer shank as on a ‘bolt’.  They all come in socket screw form these days it seems.

Using copaslip is a good solution to the problem of them sticking,  Don’t use oil, the screw may vibrate loose.  A small tube will last for years if used for it’s purpose.  A good substitute believe it or not is soap.  Wipe the screw on s piece of wet soap before fitting.  That also prevents woodscrews from sticking by the way for those DIY ers out there.

A precautionary tale.  I bought an ex school Boxford lathe, in rather good condition as it had little use, a bit bashed but little wear where it counted.  However I noticed that the main drive pulley (10 inch dia) was distorted and not running true.  When questioned, the workshop technician told me that they had to remove the pulley for maintenance in the past and although they had removed the retaining grub screw it would not shift off the shaft no matter what.  he claimed that it ‘must have welded itself onto the shaft’.  Eventually they resorted to a hide mallet, hence the distortion. 

 

What they had not known is that Boxford, like many other companies in the past used two grub screws in each pulley boss, one on top of the other.  The first one locks the the pulley to the shaft and the second is locked down on top to prevent the first from vibrating loose. Much in the same way that a locknut is used on a screw thread.   So, after removing a grub screw always check that there is not another little bugger hiding down there to cause trouble.  Before reaching for the biggest mallet you can find by the way.

[KWILParticipant @kwil]

Reference to the original Myford Handbooks would have told you that ML7 series lathes had 1/4″ BSF x 5/16″ cup point  socket set screws in the motor pulley,  Myford Super 7 had  a cup point socket set screw of the same dimensions but with “wedgelok” insert or a longer [3/8″]  cup point socket head setscrew. Later Power Cross Feed machines were similarly fitted. Interestingly the text in the handbooks refer to the said “set screws” as grub screws when giving instructions as to how to fit and mount the motor!!!!!

 

Fully threaded hex heads are machine screws as opposed to part threaded bolts and are also refered to as Set Screws, and socket set screws are also called grub screws, it all depends on where you look and which supplier!

[Ian S CParticipant @iansc]

Socket head fully threaded bolts are also called cap screws.On old machinery offen agricultural offen has set screws holding pulleys etc these being fully threaded with square heads,b****y menace.Ian S C

[Ian S CParticipant @iansc]

Just an idea I had,if you use one grub screw or two in line,you have two points of contact opposite each other(not stable)used a 120deg gives a stable fitting,you could put two grub screws at these points.Ian S C

[Goran HosinskyParticipant @goranhosinsky61367]

 “A good substitute believe it or not is soap.”

Would that work for steel pulleys too? 

[Ian S CParticipant @iansc]

Sometimes a whack with a hammer and punch that fits inside the hex socket will free a tight grub screw.Candle wax also may be used as lubricant for screws-wood or metal,alsoon saw blades from fretsaws to crosscut or hacksaws.Ian S C

[Gordon WParticipant @gordonw]

The old agri screws with sq. heads – brill. spanner doesn’t slip on them. In the olden days, when I was young, the socket head screw makers published loads of data, one book had several pages of info. showing transmitted torque for different angular disposition of grub screws round the shaft, the closer together the better! One opp. the other in some cases less than one screw. Two in line best (for power transmission).

 A bit OT ,I can remember one maker, Unbrako?, had a tool for sale which peened the sides of the head counter bore into the grooves on the head, so locking the bolt. Can’t find the ref. now, anyone remember these?

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