Boxford back from the dead

[Sea.dog]

The large backgear is a press fit, at least it is on my spare. You may have a mix.

14.5° gears have a rounded root whereas 20° is flatter, or is it the other way around? Whichever, you can see the difference between the two from both the root profile and tooth profile.

[AdeV]

Hi Seadog -

Yes, it's a press fit on mine too, with a thin (1/8" maybe) round pin serving as a key to prevent it rotating on the shaft. I know it's a very light press fit as I can move it a little if I push hard on the shaft with my thumbs whilst holding the large gear...

Turns out, it's not as easy to get hold of plasticine in the shops as I expected it to be.... so I've had to order some instead. Along with a protractor (10 off!!!) and an angle ruler which I may or may not find a use for one day. So tonight I'll have to make do with using the Mk1 eyeball, or maybe I'll just rest up tonight. I may need to plan some more purchases for the weekend...

[Fergus OMore]

Blu-Tack? I don't like stealing from grand children

[mattinker]

Turns out, it's not as easy to get hold of plasticine in the shops as I expected it to be.... so I've had to order some instead. Along with a protractor (10 off!!!) and an angle ruler which I may or may not find a use for one day. So tonight I'll have to make do with using the Mk1 eyeball, or maybe I'll just rest up tonight. I may need to plan some more purchases for the weekend...

I use plasticine when casting in plaster etc. I usually have three or four kilos in stock! I buy mine from a supplier of casting materials, resins, fibre glass matt etc. Artists suppliers should stock it!

Regards, Matthew

[awemawson]

Dig a hole in the garden, surely Liverpool is on clay ?

[AdeV]

Dig a hole in the garden, surely Liverpool is on clay ?

I'm not in Liverpool, I'm in Birkenhead - which is mostly on used engine oil 

[AdeV]

Artists suppliers should stock it!

Never thought of that - I was looking in toy shops 

Fortunately, Amazon to the rescue, I've got 1/2kg landing at Lime St. Station tomorrow (in time for me to pick up on my way home after work), for the princely sum of £4. I could have had it for £2.85 if I wasn't so impatient... Had to buy a pack of 10 protractors to get next day delivery on them too  Anyone want a protractor?

[AdeV]

14.5° gears have a rounded root whereas 20° is flatter, or is it the other way around? Whichever, you can see the difference between the two from both the root profile and tooth profile.

I can't honestly see any significant difference between the two. It seems unlikely the one actually stamped 14.5PA is lying.... but one never knows. All the gears all seem to mesh with each other just fine... even the ones that aren't supposed to (e.g. the bull gear and the gear on the end of the pulley unit; or the pulley gear on the small end of the backgear shaft.

My backgear shaft has one damaged tooth... so it's tempting to cut a new one to 14.5PA, assuming that matches the bull gear of course.

[Sea.dog]

At the end of the day, if you're using the back gear on a regular basis then you're going to wear both gears. If it's only ocassional use then you will probably get away with it.

[Pete.]

Any gear you can lay flat on paper can be checked for pressure angle. Download Geardxf.exe which will generate a dxf based on your inputs. Generate gear drawings for both pressure angles. Now open the dxf's in a cad program and print them side by side it at 1:1.

Simply put your gear on the drawing and see which one it matches best.

[AdeV]

Well, the plasticine and protractors arrived 

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  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... 

[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  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    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  ).

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  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  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! 

[awemawson]

Excellent machines aren't they Ade 

A distinct sense of de ja vu seeing that reminding me of making a big socket grub screw for my folder

[AdeV]

Excellent machines aren't they Ade 

They certainly are! Pretty specialist... but for this kind of job, indispensable I'd say!

A distinct sense of de ja vu seeing that reminding me of making a big socket grub screw for my folder

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...)

[awemawson]

Yes but only a few thou

Detailed here:

http://madmodder.net/index.php/topic,9334.0.html

[kayzed1]

what size of CI do you need for the gears?

[WeldingRod]

You can broach blind, but you have to keep pulling the tool out as n breaking off the chips with a punch.  That's how I made the cams for my D-1 headstock mod.
I might still have the backward one ;-)
Yep!

Sent from my SAMSUNG-SM-G891A using Tapatalk

[AdeV]

what size of CI do you need for the gears?

The OD of the large gear is 4", the spur gear is about 1.6" ish (I have the exact measurements, but not here). I was going to buy a couple of slices of 5" CI for the big gear (4.5" doesn't seem to be available), and a 2" bar about 6" long for the spur/shaft. The main thing that's stopped me is I'm not sure how to bore that large a piece with sufficient accuracy... the original looks to be a casting, with both ends machined about 2" in, with the centre left "as cast", with a smaller diameter. I don't know if they cast it as a gear & then tidied the teeth up, or as a blank & fully machined the teeth into it.

The large gear is about 0.580" thick, although I assume that's not a particularly critical dimension.

[Pete.]

If you're making a 4.5" gear from raw cast bar stock you'll need to start with a  5" bar anyway. The outer crust can be quite thick and you won't want to be cutting teeth in it.

[AdeV]

If you're making a 4.5" gear from raw cast bar stock you'll need to start with a  5" bar anyway. The outer crust can be quite thick and you won't want to be cutting teeth in it.

Good to know, thanks. I was going to buy 50mm bar for the spur gear (which is as good as 1.625" OD, or a shade over 41mm), suitable do you think?

I snuck down to the workshop today for half an hour (have car, will travel... but my knee is basically better now, so I won't have an excuse to drive to the railway station for much longer), so I cut the hex into the end piece, and using a fairly coarse file, cut a bit of a dome in the end. The belt sander tidied up the worst of the machine marks on the faces, so I brought it home and had a go at polishing it  OK... I need to do more work on getting rid of the cutting marks, this was just playing around really. It still came out nice and shiny, which is what I'm looking for. Mmmmm. Shiny.

Now.... do I gold plate it for the "black and gold" colour theme.....? 

[AdeV]

  I just realised I'd got the old bit here too, and the part it fits in. And as we know:
 

So may I present: Old vs. new; old in the mating part; new in the mating part 

I still need to drill the handle hole (should be straightforward enough), and the hole for the grub screw. The latter will wait until I've got the shaft finished, so I can be sure the end of the grub screw fits perfectly. Also note, I've made the hex a bit bigger - 3/4" instead of 11/16". I can never find my 11/16" spanner... but 3/4" = 19mm = loads of them kicking around the place 

[AdeV]

Things have been a bit quiet on the Boxford front the last few days; I found myself short of tooling... After several abortive attempts to cut a thread using a brazed carbide tool (chipped the end off), an insert (wouldn't go deep enough, and I'm 99.9% sure it was a 60 degree bit anyway), I did finally get some success with a ready-cut HSS tool I found buried at the back of a box of HSS bits somewhere. I think it's 55 degree, but it's hard to be certain. There's not a lot in it, and my eyes aren't what they used to be. If anyone has an easy way to determine a 55 degree vs. 60 degree cutting tool, speak now... So... more on the threading tomorrow, when I hopefully finish off the belt adjustment shaft.

Meanwhile, a set of polishing wheels/polish had showed up, and yesterday a fine selection of wet & dry paper in various grits (all the way up to 3000!) appeared; so tonight I called in at the workshop for a bit of messing about. Basically, I wasn't happy with the finish on the adjuster collet thingy, so I chucked it up in the lathe, and filed away the worst of the indentations. Then I used progressively less aggressive emery cloth - 80 to start, then 120, then 240, followed by some 400 grit W&D, finishing off with 1000 grit. I did the same with the adjuster nut/handle holder thingy, although I've not yet done the flats (I'll drill it first).

Finally, when I got back home, I gave it a 2 stage polish on the hard cloth wheel & then the soft floppy wheel, with the two grades of polish which came in the kit.

I think they came out rather nice. If you look really closely, there's still a few scratches left from the sanding (they may not be that visible in the photos)... but they'll do for me, for now 

[Sea.dog]

You need one of these, Ade.

[AdeV]

I do have a fishplate (somewhere - can't put my hand on it right now....), but I find even that difficult to use, especially if the tip of the tool is small. Hm, I wonder if one of those digital protractors would do the job.... Now, where did I put my Amazon catalog?