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| Question about chucking a large part in a lathe |
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| Lew_Merrick_PE:
Spin, Back in the dark ages, we used to set-up a blank on the surface plate such that we could use our (triangular edge) precision square to set the part perpendicular to the surface plate. We would then cast in some zinc to create a planar face for mounting. I have also performed this trick using plaster of paris. The advantage of plaster is that a sheet of waxed paper serves to protect the surface plate. The disadvantage is that the resulting "base" is quite brittle. You can do the same thing with epoxy. Does that help? |
| loply:
Can you not make up a suitable arbor and mount it on that? |
| Jonny:
This is one thing i do almost daily, well over 700 items. The o/d of the aluminiunium for starters wont be round! So you hav eto take some off the o/d after the bore has been put in. I normally use a 3 jaw chuck with sawn cut blank placed in. True up by eye or use tool tip. If need be get the burr or larger thicker in between two jaws then take a facing cut, thats your working edge. Remove from chuck and turn around, machined face up against the jaws, but check runout. Action shot with small 6" chuck 11 year ago |
| SPiN Racing:
Quite a lot of methods! As it turns out I tackled things tonight with my 10" 4 Jaw independent chuck. I used a machinists SQ and siscovered each one was a tad over .1 out of whack. Soooooo SInce there were saw marks from the bandsaw they used to lop off the slices..in the 4-jaw, with a .1 spacer in the one jaw, between the piece and the jaw. Then I got the jaws in the ballpark... THenb got a dial indicator and indicated Each jaw, till the pairs of jaws were symmetrical to each other. Yep Jonny was correct.. its NOT round. LOL Turns out the opposite sides were off by around .02 SO as long as I got them true to each other, it was square? Then I went ahad and put the dial indicator onto the piece.. right in front of the jaws.. and then went through more fine tuning of the positioning.. seems my 4 jaws are not exactly the same. Once it was re-re-re-centered.. I then was able to put the dial indicator adjacent to a jaw.. then move the cross slide.. away from the chuck, and I was getting ZERO movement, letting me know it was square on all 4 jaws. Once the first side was faced, it was a breeze to flip and re-center it. Standard 4 jaw methodology. (But I did quadruple check the measurements) Drilled the center hole, and then began boring the center out to the dimentions I need. I also have a arbor I will be able to mount the chunk on once its center id bored. THen it will go over to the mill and get the periphery holes banged out of it. I will take a couple Pics tomorrow. :) |
| Jonny:
Happy your sorted, luckilly most of what i do doesnt 'have' to end up cock on o/d, so can afford to take a skim off o/d when bores in. There can be swage or draw marks in aluminium round, just had a look at the 120 blanks just collected larger than above piccy dia, they look ok. Whereas the other 100 or so older blanks some have really pronounced draw marks and may need 2mm off o/d. Or even dinks. Cant you grip through the bore with 3 jaw and use tailstock other end? Its the only way i can do above quick. |
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