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| How do I....bore out a hollow section leaving the centre intact? |
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| AdeV:
--- Quote from: Darren on December 22, 2009, 10:21:20 AM ---Bernd is correct, the bottom part is in fact two parts one of which is a normal Allen headed bolt. :thumbup: --- End quote --- Aaaahhhh, sneaky! :bow: However, I do have a problem with getting both ends exactly flat & at 90 degrees with respect to the sides; I can do one side easily enough, but if I have to unchuck the work, I'm buggered, because I'll never be able to guarantee getting it exactly flat & concentric. OK, I can use a parallel in the chuck to get close on the flatness... would that be enough? I've found with my 1st arbor attempt that the bottom piece doesn't run true when the saw is in place - but it DOES run true when the saw is left off... implying it's one (or both) of the holding faces that's out of true. Andy - I'll check that out on my 4-jaw. It'd be great if that's the case :) I just have to make the chuck key first.... |
| Darren:
1, Turn down the shank that fits into your arbour on the mill. (mine was 20mm) 2, turn the part around and machine all the steps and thread the end, 3, finally face the end of the first part and de-bur. 4, face another piece if the stock, drill centre through to match bolt size for first part. 5, bore centre out to match the boss on the arbor. 6, remove second part from chuck and fit it to the first part and re-chuck the first part. 7, Now face off the second side of second part. I suppose you could make the second part first so the first part never needs to be removed from the chuck until the whole job is finished for even greater accuracy. Like the cups trick you need to keep in mind which is the first and second part all the way through not forgetting if you swap the order they are made the first part becomes the second part and the second part becomes the first part respectively. Just read it again ... slowly :lol: :lol: :lol: |
| AdeV:
Your steps 2 & 6 cause problems for me... as soon as I remove the part from the chuck, it's a dead cert it won't go back in without runout and/or wobble. If I had a collet chuck, then I'd have no bother following your instructions, 'cos the arbor could be chucked in that once the shank was cut. The way I made the part (or, would have done, had the bore cutting worked) was as follows: 1) Face & turn stock so it's running true & faced flat. Turn down to main arbor size (1.5", or maybe 1.25" for Mk2). 2) Centre drill, drill, ream a 3/4" deep hole to accept a suitable thread (I chose 1/2" BSW, as I have both taps & dies for that). Cut about 1/4" to clearance size, then tap the remaining material in the hole. 3) Turn a small portion of the end of the stock down to 1" to hold the saw. Once close, take fine cuts & test the fit often. Face the outer section to ensure it's flat. 4) Use the cut off-tool to make a couple of relief areas at top & bottom of shank. Turn shank down to size, then part off. 5) Turn down about 1/2" to the appropriate size for your thread. Cut threads as close to the shoulder as possible (I cheated: I cut them to 0.040" depth, then finished off with a die - this left quite a loose fit thread which I wasn't that happy with). Bore out some stock around the thread, to an outer (inner?) diameter of 1.003" or thereabouts. It should fit neatly over the saw, without too much slop. This is the bit that failed for me... 6) Once you're happy with the fit & finish, screw the two parts together & turn the outer diameter to whatever you're happy with (did that bit in Step 1!). Remove the first part, then part off the 2nd part from what's left of the stock. Job done! If I can make Step 5 work, it never needs to come out of the chuck, which should guarantee next to no runout (less than 0.001"). I do need a left & a right handed turning tool (only got RH tools in the toolpost just now) |
| Darren:
I suppose I'm fortunate in having an accurate 5C collet nose in the spindle. Another option would be to use the four jaw and dial it up true. |
| John Rudd:
Unless I'm mistaken.... The important part is the shoulders for the saw blades being concentric to the diameter of the main body....The retaining part doesnt matter...its only for aesthetics.. Having made a saw arbor( spelling?) I noticed that saw blades dont run true any way...... |
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