The Craftmans Shop > New from Old
Boxford back from the dead
AdeV:
Well, the plasticine and protractors arrived :clap:
After a fair bit of mucking about... I figured the easiest way to check this would be to squidge some clay into a tooth of the bull gear, cut away all the surplus material around it & then very gently extricate it. Using this perfect(ish) tooth form, I then test-fit it in all the other gears. The results are: The pulley gear is 14.5PA to match the bull gear. The backgear shaft has 20PA gears on both ends.
As this is clearly unacceptable :palm: and assuming original 14.5PA backgears for Boxfords are either unobtainium, or priced accordingly... I shall obtain some cast iron and make a new set.
Looks like the dividing head I bought mumbleteen years ago, which has so far only been used for cutting hex ends on shafts (I can hear it crying from here), will finally get used for a proper dividing head job! I bet I can't find the right plate... :scratch:
AdeV:
Another weekend plagued with visitors means not as much achieved as I'd hoped... but at least I made a start on some of the repairs and new parts.
So... now I'm wishing I hadn't used quite as much superglue on the headstock as I did :palm: That stuff does NOT react well to being welded through... I managed to get a few tacks to hold, though... before blowing the top out completely :bang: So I left that for another weekend, and moved on to the new belt tensioner parts. The shaft should be relatively straightforward, but I wanted to make the front piece (the one that takes the handle) first, then I can make the hex end of the shaft to fit that part.
1st effort got abandoned due to me making some dumb mistakes with my measurements, the second effort was much better. It's made of some mystery steel which hasn't got a nice finish on it, but I'm hoping it'll polish up OK. The turning was straightforward and not worthy of pictures; where it gets interesting is cutting the hex hole.... so finally, I get to use my spark eroder on a real project (well... for certain values of real anyway :lol:).
First job, after finishing the steel blank, was to turn a piece of copper bar down to the appropriate diameter (pic 71 & 72 - the poor dividing head mentioned earlier, still just cutting hexes!). The slightly smaller diameter on the end is a registration diameter, and just fits in the hole drilled in the steel. This will allow me to line everything up on the spark eroder, which doesn't have graduated handwheels.
Pics 73 & 74 show the copper electrode with the hex cut finished to a high-ish polish (ahem).
Next, the steel blank is clamped into the spark eroder, the electrode tightened into its holder, and the whole lot lined up (pics 75, 76), then the tank is filled and the eroding begins (pic 77 - which is about the best shot I could get. Photographing spark erosion from above the fluid is really tricky! I just remembered, as I write this, that I have a GoPro-like camera with a waterproof housing.... so maybe I'll try for a submerged shot from that next time. Watch this space!)
AdeV:
After a couple of hours, I checked on progress, which was really good - about 0.8" done. At this point, I discovered that the adjusting nut for the electrode was interfering with the clamp screw. One issue with a spark erosion machine... it'll cheerfully eat itself, without giving you any warning signs! Another issue, the electrode also wears, as well as the workpiece; so having to re-arrange everything inside, I also took the opportunity to lop the worn bottom off the electrode. I no longer needed the registration round, as I could use the hex itself. After this, another couple of hours of fizzing and popping, I called it done.
The remains of the electrode (pic 78) show clearly how far in it got; also, if you look at the bottom, you can see it's worked its way back to being round... However, there's still about 800 thou of decent hex left, which is plenty deep enough for my purposes. If push absolutely comes to shove, I can always chop the bottom off it again, and use the as-yet unused bit to push the hex deeper. Pic 79 gives you some idea of how deep into the part it's gone. That's at least 3 diameters...
Pics 80,81 are the money shots :lol: I reckon broaching is the only way to get a better hex, and I'm pretty sure you can't broach into a blind hole and get all the way to the bottom of it without some really fancy-pants way of getting rid of the chips....
Finally, pic 82, just to show the bleedin' obvious; the electrode fits perfectly in the hole :bow: There's probably about 3-4 thou clearance all around, which makes sense; it also means I'm not exactly sure how big it is, except that it's a smidge bigger than the drawing calls for... this is why I wanted this part made first; I'll cut the hex into the end of the actual adjustment shaft next, and will sneak up on the final dimension so it's a nice wobble-free sliding fit. At least... that's the plan! :coffee:
awemawson:
Excellent machines aren't they Ade :thumbup:
A distinct sense of de ja vu seeing that reminding me of making a big socket grub screw for my folder
AdeV:
--- Quote from: awemawson on June 24, 2019, 05:57:57 AM ---Excellent machines aren't they Ade :thumbup:
--- End quote ---
They certainly are! Pretty specialist... but for this kind of job, indispensable I'd say!
--- Quote from: awemawson on June 24, 2019, 05:57:57 AM ---A distinct sense of de ja vu seeing that reminding me of making a big socket grub screw for my folder
--- End quote ---
Out of interest, did you under-size the electrode for your grub screw, so the allen key was a good fit? If so.. approximately how much undersize did you need to go?
Cheers!
Ade.
(Hmm... I should get back to work...)
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