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| andyf:
Hi Wong, It would be easier to use threaded rod. I assume that you will need an M10 thread. The head will be so large that making the drawbar out of bar stock would waste a lot of material. To avoid having a separate nut, you could make a big M10 nut, and experiment to find where it needs to be to get the drawbar to the correct length before cutting off the excess rod and welding or brazing the nut permanently in place. Making a bolt-on collet chuck shouldn't be too difficult. I don't think you need to buy one with a Morse taper shank to copy. The taper is 8 degrees (16 degrees included angle) as shown on the drawings here http://www.arceurotrade.co.uk/Catalogue/Collets/ER-Collets-Collet-Chucks . Test the taper with a collet into which you have inserted a bar of the maximum size it is supposed to hold (for example, a 6mm bar in a 6 to 5.5mm collet) so the collet can't compress as you push it in. Make the chuck a bit too long, and then trim back the outer end so that about 2mm of the 8 degree taper is projecting. That will allow each ER11 collet to operate over its 0.5mm gripping range, though I see that Arc Euro's largest ER11 collet has a 1mm range (7mm down to 6mm), and that would need to have about 4mm projecting. If you can find a 6.5 down to 6mm collet, that would be better. Andy |
| wongster:
Hi Andy, I've not tried brazing before. I've this proxxon torch that can generate heat up to 1200C. Can this be used? I tried looking for those bigger cylinder type shown on some pics here and on youtube after reading about brazing and silver soldering here. Those places I frequent for machining stuff don't carry them. On setting the angle on using the compound, I'm not sure how accurate is the scale on the lathe. I tried turning to a 60 degree point (setting the compound at 30 degree). When I measure the resulting work using a made in china angle gauge, I was off to almost 1 degree. Is this acceptable for the taper? I'll see if I can find a more accurate angle gauge and do some more test cut to get a feel. Regards, Wong Edit: I found a simple article on a robot making site. Saw from the pics that they used similar kind of torch I have. I'll source for the other things needed when I've time to go shopping. Likely after the Lunar New Year, which is just next Monday. |
| andyf:
Hi Wong, 1200°C is hot enough for silver soldering/brazing, but the nut will be fairly large, and a small torch might not be enough to get all of it, and the threaded rod inside, up to red heat at the same time. It would be easier to take the job to a welding shop. You want the top slide to be as near as you can get it to 8° before cutting the taper, leaving only very fine adjustments to be made (if necessary) after testing with a collet and marking compound. Use trigonometry and imagine a triangle, angles of 90°, 82° and 8° as its angles. If the side opposite the 82° angle is 100mm long, then the side opposite the 8° angle will be 14.05mm. Bring a plunger dial indicator to bear on the side of your top slide, and adjust the angle of the slide until the indicator shows a movement of 14.05mm when the whole carriage is moved along by 100mm as measured by the leadscrew handwheel and its dial. Be careful to take up any slack between the half nuts and leadscrew as you measure the 100mm. The 100 and 14.05mm can be scaled up or down to suit the length of your top slide. Scale them up if you can, because that will give greater accuracy. Of course, this assumes first that the indicator plunger is at 90° to the lathe bed, and secondly that the side of the top slide is parallel to the dovetails within it. The latter seems to be true on my Chinese lathe and it will probably be true on your German machine. Andy. |
| wongster:
Hi Andy, Thanks. I'll experiment a little. Will post pics when I get there. In my last session in the shop a few days back, I managed to remove the little key on the feed screw of the cross slide. It wasn't as tightly pushed into its slot as I thought and thank God it didn't fly... :) I give the feed screw a thorough clean up with a soft brush (old tooth brush) and apply way oil on it generously. At the same time, I adjusted the gib screws while sliding the slide in and out without the feed screw installed. It now slide nicely though I still have movement when I push the slide along the feed screw. Backlash? I don't have that on the compound and I ensure that the hand wheel nut are tight enough. So far it hasn't caused any problem when I did facing cut or parting off. Regards, Wong |
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