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Holding square bar

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Andy Freeman 1	30/09/2011 22:17:45
50 forum posts 33 photos	I have a 8mm square bar, 1m long. I need to machine a narrow 2mm groove 15mm in from each end. I do not think it is a good idea to just hold it in a 4 jaw chuck and leave the other end un-supported. I thought I could hold one end in the 4 jaw chuck and the other end in a similar small 4 jaw chuck that could also rotate in the tail stock. Is there such a chuck? Anyone have any other ideas how to hold this? Thanks for your help
Jeff Dayman	30/09/2011 22:35:57
2356 forum posts 47 photos	The simplest way would be to centredrill the bar end with a portable drill, after marking and punching centre of the bar. Rest the centredrilled end on a live centre or dead centre in the tailstock. If you can't centredrill it see other ideas below. You can get an inexpensive Chinese made bell centre - this is a live centre with a funnel like socket rather than a centre conical point. The bar end would rest in the socket at 4 points but you may not have tool access to make your groove if funnel is deeper than 15 mm. If you go this route get a shallow one. Chronos carry them I think. If you have a steady rest you can also use a cat head. The cat head is a piece of pipe (or a close fitting drilled round bar part that fits close to the square bar corners) with 4 screws in tapped holes at 90 degrees to each other. They come out of the pipe like spokes in a wheel. You slip the cat head over the square bar, tighten the screws so the bar runs true to the pipe OD, then rest the pipe in the steady rest which supports it while it turns. Hope the info helps. JD
Nobby	30/09/2011 23:16:44
587 forum posts 113 photos	Hi And If the bar goes through the lathe spindle . Turn up a bush with a shoulder Say about 1/2" Dia. bored through with a hole so that the square corners fit . Then split it . Then you can use it in a 3 jaw sticking out minimum to do the job . It may need some support if it sticks out the end of the lathe. I use this but the back end of my S7 mk 1 is near the shed wall so i have a hole there and long items sticks out side But it acts as a steady Nobby
Les Jones 1	30/09/2011 23:23:56
2292 forum posts 159 photos	Hi Andy, I would have the long part through the headstock with about 25 mm sticking out of the chuck. The part sticking out of the headstock I would support in a length of tube. Run the lathe fairly slowly so it does not rattle round in the tube too much. Les.
NJH	01/10/2011 00:18:54
2314 forum posts 139 photos	Hi Andy A rotating tailstock holder for a Myford chuck is available from RDG although this might be an expensive option for your process. Norman
Les Jones 1	01/10/2011 09:25:07
2292 forum posts 159 photos	Even if the lathe is long enough to take 1 M between chuck and tailstock I think it would still need a steady about half way along. Les.
Gordon W	01/10/2011 12:04:52
2011 forum posts	Assuming the bar will go thru' the spindle, do as suggested and use a length of pipe to support the sq. bar. I've just used a cork to stop the rattles, but do run slow.
Maurice	01/10/2011 20:32:28
469 forum posts 50 photos	I made up a rotating four jaw chuck for the tailstock, using an old "Unimat" 4 jaw independant chuck, a morse taper blank, an off cut or 2 1/2" steel bar,and a couple of ball races. It was specifically to machine the connecting rod casting for the "Major" beam engine from Stuart Turner; it was a total success. Since then, it has been very useful on a number of occasions. I did see all the parts one would need to make a similar one, in one of the free tool catalogues that sometimes arive with our mgazines, I'm not sure who the supplier was, but I will try to find it if you wish, Maurice
Steve Withnell	01/10/2011 22:06:49
858 forum posts 215 photos	I can't imagine doing this between centres It'll be like a skipping rope! The right way IMHO is to shoot the bar through the spindle and I think Gordon's idea of using a piece of cork in a tube supporting the free end sounds spot on. An old pal of mine needed to cut a keyway on a 12 foot long propshaft for a boat. The lathe was in the shed, the free end supported in the kitchen...
Richard Parsons	02/10/2011 14:48:37
645 forum posts 33 photos	Andy You say about a 2mm deep grove. Is this ‘across the flats’ or across the corners. I presume it is for a surclip. I would be inclined to bore up a bit of steel so that it fits your bar snugly across the corners. I would arrange a 2mm wide tool with a feed screw 15 mm from the bottom of the bit of steel. Turn it by hand or fit a stub to it and spin it in a drill.
Andy Freeman 1	09/10/2011 19:44:31
50 forum posts 33 photos	I thought I would post again and thank everyone for their ideas. I ended up drilling a hole throught the wall of my shed wall to support the square bar as it rotated. It worked well. Running at a relatively slow speed I was able to turn the grooves, which were actually only reducing the 8mm square bar to Ø8 If anyone was wondering what it was all for..... well it was a barbacue rotisserie spit thing for my friend. After all this on the day it rained so he didn't have the barabacue. Oh well, maybe next summer!

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