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| NickG:
Stew, Thanks but I think I rushed into boring the stand too much. I should maybe have made a custom boring bar. That one was too long and the v type tool that was already in it was no good - I think the angle started pushing, bending the bar rather than cutting cleanly. I fed it with the drill feed too which was too fast, maybe I should have fed it down with the spindle just nipped. Maybe the tool wasn't quite sharp enough either. Whatever I did, didn't seem to work very well at all. I don't think I need a boring head for the amount of times I do this, although guess then I could quickly and accurately bore to a good finish. Does anybody have any other tips for boring like I did? Thanks Nick |
| madjackghengis:
Hi Nick, you're looking good there, getting along well. The boring bar issue is almost always about the cutting tool. Boring is inherently about doing something you need with the worst possible conditions of tools in that you have the longest tool holder, supported on one end only, and you're working inside, so you need extra "front" clearance on the bottom end of the cutter, to clear the circumference sector between the cutting edge, and the heel of the tool. If the tool has a "shear" cutting edge, from a fair top clearance angle, appropriate front clearance, and like you said, going at the work pretty close to square on, with a nice radius, minimum size, fine finish, and the bottom of the cutter radiused for the clearance you need, and of course, the cutting edge back relief such that the edge is cutting "on plane" with the centerline of the spindle, you can expect a good clean bore. The usual bit that's missed is the heel of the cutter, with it dragging through the already cut part. Making sure your cutter has a smaller radius from top, cutting edge, to bottom, trailing, than the hole being bored will ensure this doesn't happen, unless your cutting edge is above the "plane" of the spindle centerline. I use a fly cutter holder, with a tool ground to meet all the angle requirements to fit in my boring head, for boring Harley engine cases larger for big bore cylinders, and have tool bits just for that specific job. A through cut, such as you've taken, can use the same form of tool bit a between centers boring bar uses, with the same parameters, angles and nose radiuses adjusted for the metal being bored. I hope this helps a bit. With regard to cutting the slots for the crank, you can cut such a wide slot by cutting most of the way through and leaving fifty or sixty thousandths in the back of the cut, taking both cuts, to get your width, and then do the final cuts from top and then the bottom, so you have support to the end. You can even cut the last out by hand, and even up the slots with a hand file. :bugeye: mad jack |
| NickG:
Thanks madjack, I will follow this reply next time I bore something in the miller to get the tool correct. I've just been looking at the poppin plans and it'd been so long since I did the cylinder I forgot, it's actually 5/8" bore! So I probably could have left the bore in the standard 5/8". I doubt the con rod comes within 1/32" of the bore in the standard so see no reason why it would need to be larger than 5/8". :bang: Just been compiling a list of what I need to do to complete an engine - it's bad enough for 1 engine, let alone two! I definitely want to finish both at some point though as if one goes to my Dad for his birthday in March, I want the other for my collection of engines. I think I have 7 nights work left so that means if I manage to get workshop time every night, one should be ready for next Tuesday - quoting timelines always puts the kibosh on things though! Nick |
| arnoldb:
:thumbup: Good progress Nick :D Before I built the boring head in my avatar, I had to do boring with bars similar to yours. It takes a fine feed and not too great depth of cut; you can't hog it. And a very sharp cutting tip helps as well, with suitable clearance on all sides. It takes a bit of patience - and gets a bit ..erm.. boring :palm: :beer:, Arnold |
| NickG:
Ha, nice one Arnold :lol:. Come to think of it, I had a 5/8" hole and I tried to take it out to 11/16" in one cut - that's 31 thou so quite a bit I guess, esp with the wrong, blunt tool and too much sticking out of chuck. Your boring head looks great by the way. Didn't get much done tonight, was basically messing around but nevertheless did a few jobs that needed doing. I cut the shaft away from middle of crank, drilled and tapped the holes in the base, tapped the holes in cylinder to mount and for cover, drilled and tapped the hole for the oiler, cut some bolts to length and assembled some bits. Here are a couple of pics of the assembly. It's only now that I get a feeling for the size. I love the look of the engine but the more I look at it the more I realise it's not particularly well made. I just really hope it's going to work! Will just have to make sure I get all the critical bits right again. Quiz night at the pub with mates tomorrow so there won't be any progress until thurs night now, hopefully i can crack on and get some bits made now some of those fiddley jobs are out of the way. Nick |
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