Sheared Drawbar

[Steve Taylor 2Participant @stevetaylor2]

I have a 2MT Carkson collet that the drawbar has sheared off. The end in the collet taper is stuck firm, very rough, extremely hard and broken below the end of the taper.

I cant drill it with carbide because its not flat or mill it with HSS tooling, any ideas are welcome please.

I have seen a replacement for sale but it dosnt have the large collar (damping ring) with 3 holes for a tommy bar, is the collar essential?

[Steve Taylor 2Participant @stevetaylor2]

[KWILParticipant @kwil]

When I have had something that stuck, I turn to hydraulics before a hammer. My gear puller has a 5 ton ram and that seems to help a lot.

[David Clark 13Participant @davidclark13]

Hi There

Use a small cardbide slot drill.

Spotface a flat on the end of the drawbar.

If you can, raise the table rather than bring the quill down.

Very slowly spot face it.

You should be able to drill it out then.

Drawbars should not be that hard, they will break.

regards david

[mgjParticipant @mgj]

Steve- is this collet chuck stiuck in the machine, or is it out of the machine but with a lodger in the drawbar socket?

 

Is the collar essential – no I don’t think so. There are lots of chucks in that style that don’t nor ever did have the damping ring. So i suppose the answer is better with if possible, but don’t lose any sleep over not having it – as long as its concentric etc. Or you can machine the ring yourself.

 

If its not stuck in the machine:

Can you grind the end flat – or flat enough to drill. It won’t matter if you lose a bit off the end of the taper. Not too much of course.

 

Worst case, and you really really can’t drill it, heat to red heat with oxy acetylene, and let it air cool to soften it? One doesn’t at that point have all that much to lose.

 

Does anyone know if the alum trick will work.?

 

If its stuck in the machine then KWIL has the best suggestion.

 

I did get one out for someone last year with dry ice. I was looking for one of those pipe freezing kits, but I ended up with of all things, one of the Verruca freezer kits from a chemist. Took the collet out, put cotton wool in, and sprayed the liquid CO2 in from the front having got pressure on from behind. (threaded clamp and rod down the spindle) After 20 minutes it just fell out. Surprised me, but it worked well. Made by Scholls – you get quite a chunky little can of liquid CO2 in there.

 

Apologies – I have read your other thread after writing this. If one could put it politely – that  makes KWILS point rather well! Might be an idea to check the bearings?

 

 

 

 

 

 

 

Edited By mgj on 10/02/2011 19:50:09

[JasonBModerator @jasonb]

I don’t think Alum will work as it will disolve both the taper shank and the stuck thread, best kept for when steel is stuck in nonferrous.

 

I had the blade holding bolt shear on my chopsaw on tuesday, luckily the spinning blade stayed within the guard, manages to screw the remnants out with a ctr punch and light taps.

 

Jason

[Steve Taylor 2Participant @stevetaylor2]

Yes its definately out of the machine, I thought it was going to beat me.

 

I might try to grind the end down as its just below the rim of the end of the taper, if I had a carbide spot dril I would do it that way.

 

Thanks for everyones input

Edited By Steve Taylor 2 on 10/02/2011 20:05:01

[Mark P.Participant @markp]

I’ve had a lot of sucess drilling hard steel using a masonary bit TC. doncha know.

Regards Pailo.

[Steve Taylor 2Participant @stevetaylor2]

Posted by David Clark 1 on 10/02/2011 19:21:02:

Hi There

Use a small cardbide slot drill.

Spotface a flat on the end of the drawbar.

If you can, raise the table rather than bring the quill down.

Very slowly spot face it.

You should be able to drill it out then.

Drawbars should not be that hard, they will break.

regards david

 

David, how deep would the spot drill be able to go into the stub, far enough to enable a carbide drill to complete the job?

Thank you

Edited By Steve Taylor 2 on 10/02/2011 20:43:23

[JasonBModerator @jasonb]

David said a SLOT drill not a spotting drill, you just need to use the slotdrill to give a flat surface for the drill to start.

 

J

Edited By JasonB on 10/02/2011 20:51:18

[Steve Taylor 2Participant @stevetaylor2]

Sorry, meant to say slot drill, I’ve got a couple on the way. I was asking because I thought a slot drill could plunge into the work.

[IanHParticipant @ianh]

Hi,

 

Just picking up on the “damping ring” – in case you don’t read my reply on the other thread – the damping ring makes a fine puller to pull the chuck out of the taper. Plenty of chucks do without them but having one makes your collet chuck superior in that if nothing else it provide a means for you to remove the chuck without beating your spindle to death again in the future.

 

Ian

[John OlsenParticipant @johnolsen79199]

Well, if it is hard enough to be difficult to machine, no wonder it broke. If you don’t have any luck with carbide cutters, perhaps you could find someone with spark erosion facilities.

 

regards

John

[EddieParticipant @eddie]

Hi

I modified a masonary drill to remove a broken 10mm stud lower than the surface of a crankcase. Centrepunch the broken stud.

Use a smaller Masonary drill, 5mm worked fine.

Grind the bit to cut Lefthanded, used a battery drill turning slow left attempt to let it bite and the stud unscrewed. used succesfull on Mildsteel , High tensile steel and work like a charm in brass.

Eddie

 

[john fletcher 1Participant @johnfletcher1]

I once drilled a motor bike side car spring using a masonary drill, slow speed,lots of pressure and allowed the hose pipe to give cooling and flush away the swarf. Large size 5mm tunsten carbide printed circuit drills are very useful, enabling one to drill very hard steel.These drills used to be sold at Amatuer Radio events.Ted

[Steve Taylor 2Participant @stevetaylor2]

Posted by IanH on 10/02/2011 22:52:24:

 

Just picking up on the “damping ring” the damping ring makes a fine puller to pull the chuck out of the taper. Plenty of chucks do without them but having one makes your collet chuck superior in that if nothing else it provide a means for you to remove the chuck without beating your spindle to death again in the future.

 

 

Thanks for the explanation, I understand now.

Unfortunately the Centec dosnt have any flats on the spindle, only 2 C nuts at the top to adjust the backlash. The ring is also stuck tight on the chuck.

I suspect the chuck, ring and broken drawbar have been in for many years without being moved. I’ve had the machine for a year and just started to sort it out, it was filthy and I thought looking nehlected.

[KWILParticipant @kwil]

Sounds like it would appreciate some new bearings to complete the rehab job.

[Francois MeunierParticipant @francoismeunier96697]

hi,

for this sort of “job” I use the dremel with diamond tools to weaken and dislodge the stuck piece, but it may last for several CD…

Zephyrin

[Steve Taylor 2Participant @stevetaylor2]

I followed the advice and put a flat on the end of the broken part and drilled through with a 4mm carbide drill and followed this with a 7mm carbide drill.

I can now see where the thread is however I cant shift what remains of it.

I believe the drawbar is 3/8 UNF thread and requires a tap drill of 8.2mm, the most I think I can go to is about 8mm.

I dont want to buy another carbide drill if its not going to shift, does anyone have any other suggestions please.

[Roger BanksParticipant @rogerbanks33631]

Steve,

 

Now that you have a hole through the broken part, can’t you unscrew it using an “easy-out”?

[TerrydParticipant @terryd72465]

Hi Roger,

 

Pity you went to 7mm, if you had stuck at 4mm it may have been possible to drill next to the thread on both sides of the centre hole and connecting to it, thus weakening the stub which is left.The damage to the thread in the holder would have been relatively insignificant and not affected it’s use.

 

As it is could you use a Dremel or similar to grind out an area of the stubnext to the thread, leaving only the threads of the stub in one spot, creating a ‘C’ shape and weakening the stub. You could then use a thin sharp punch to part collapse the arms of this ‘C’, releasing the stub? You could even do it on opposite sides of the centre hole after all you only have about 30 thou each side to remove with the Dremel until you get to the tap drill size.

 

By the way, have you tried drilling with an HSS jobbers drill now that you have the hole, it may be that it was just the top surface of the break which was hard due to work hardening. It seems unusual that a drawbar would be deliberately hardened and not drawn to a high temper. They are usually made from a high carbon steel but left normal. After all it’s toughness that is needed in this situation, not hardness.

 

Terry

[mgjParticipant @mgj]

Are you sure the drawbar isn’t 3/8 Whit. Mostly they are in 2MT, but thats no guarantee.

 

Terry makes a sound point – you can grind or drill close up to the threads, chuck some Plusgas onto them and leave them to soak, you’ll probably get the threads out with a spike of something. Once you get a lead in, a tap will do the rest?

 

[Les Jones 1Participant @lesjones1]

Hi Roger,

If the hole is reasonably deep you could try loctighting a bar into the hole and trying to unscrew it by gripping the bar. If that does not work you could free the bar again by heating it.

Les.

[Steve Taylor 2Participant @stevetaylor2]

I’m sure the thread is 3/8 however the blank stem of the drawbar is 8mm, which it needs to be to pass through a Centec spindle.

 

Thanks for the suggestions, however I will try the Dremmel followed by 24 hours of penetrating fluid before the next step though.

 

Its obviously been broken a long time and its likely the previous ownwer broke the drawbar trying to undo it so its probably very stuck

[Michael WildeParticipant @michaelwilde12011]

When I’m ‘stud busting’ at work I go in with a drill (carefully) just below tapping size. This then usually breaks through on one side to expose the threads. I then use a small chisel or scriber to start the thread unwinding. You can then get some needle nose pliers on the loose end and peel the rest of the thread away by turning the pliers anti-clockwise. This is best done on a milling machine (I use a kearns horizontal borer) so you can get as accurate to the centre of the thread as possible. When done right the offending stud comes out in the form of a helicoil insert. Lots of penetrating oil works wonders too, especially on plant that’s been in service for 20 years and has got lots of steam ‘scale’ all over.

Edited By Michael Wilde on 16/02/2011 09:06:05

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