A groovy pulley jig

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Eric The Viking

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Note: apologies in advance to the pros, to whom this must be blindingly obvious. But I bet you all use lathes, anyway :)

Background

"This week (decade), I has been mainly renovating the upstairs bathroom..."

I hate those push-button toilet flushes. Inside they're just flap valves: they don't last very long, they don't flush very well, and they leak.

Derided by the Victorians, European flap valves were, until recently, banned in the UK because of the water they waste. But you gotta love EU directives! Now, in the UK, you'll have some trouble buying a new toilet with a traditional syphon. Remember that one when drought orders come in at the end of the summer!

But I digress. Wanting to use a proper syphon, I couldn't find what I needed as one item, so I ended-up constructing a boxed-in cistern from parts, including a traditional "Crapper-approved" syphon*. For reasons of space and layout, it couldn't be made to flush with the usual lever/handle, so I needed a different approach. The end result, after a lot of messing about was a system with cord and pulleys.

I won't go into the details here, but I needed three pulleys, two roughly 2 1/8" diameter, and one about 4" wide. Problem #1 was that I don't have any sort of lathe, so cutting out the circles was in itself interesting. Let's just say I didn't use any sort of traditional jig.

That story too is for another day...

"Well children, here are some wooden/MDF/ply circles I made earlier. Now we want to groove them, don't we." Peter Purves

Had it been some sort of pattern, for example an ovolo or bevel or rounding-over, I might just possibly have done it with the disc flat on the router table. There's probably some expensive cutter out there somewhere with a sideways facing "V", but I don't have one, didn't want to shell out for one, and had plenty of scraps of material to experiment with.

So here's what I came up with:
pulley-groover-1.png

Construction details
Basically, it's in two parts:

  • a flat 'back plate' (pink) that is held against the router table fence with a couple of clamps (where the "X" marks are). The bottom of it has a bevelled edge, and there are a pair of parallel pegs sticking out, toward the front of the table, and close to the table surface. The pegs need to be fairly close together and of reasonable diameter (1/2" is probably about right).

  • another plate (blue), a bit smaller, bevelled on the bottom edge (at the back) and with a couple of holes to take the pegs from (1). It has a batten sticking out toward the front, glued into a notch, so that it lays flat on the router table (clamped at "X" again).

Thus you can slide the front plate assembly onto the pegs, and adjust it, then clamp the batten down to lock it in place, thus:
pulley-groover.png


There are four other significant things:

  • I have a Trend T11 that has a buit in micro-adjuster for cutter height. Any kind of micro-raiser will do, as long as you can get to the adjuster in use, but you do need to do this. The jig wouldn't work with a pre-set height adjustment, and might fire discs across the workshop if you got it wrong.

  • The cutter used is a cheap "V" grooving cutter. You could use a semicircular one (what Wealden call a "Core Box" cutter), or whatever you like, but you might want to do the setup with a v-groover, for setup accuracy and swap over for doing the actual cut.
    You could even use the jig for putting an asymmetric rebate (lip) on the edge of a disc, but the straight flute cutter would take chunks out of the two alignment plates - that probably doesn't matter, though it would affect re-using the jig afterwards. For "V" grooves, it's not critical to centre it exactly, unless the angle of the groove needs to be precise.

  • The pegs used are simply bits of 15mm copper water pipe, Araldited into place. Scrap would do as long as it's clean. This is because pipe is smooth and dimensionally accurate, and shouldn't hurt a TCT cutter if anything goes awry. And a 15mm Forstner bit is part of Axminster's nice, inexpensive set :)

  • I have a finely adjustable basic fence on the router table. This is necessary to get the cut V-groove positioned centrally on the edge of the disc (see below).


The gadget in use

It's fairly obvious really:

  1. Clamp the back plate into place, with the cutter centrally positioned between the two pegs but down below the table-top. Cutter height doesn't matter for this stage, and it doesn't have to be perfectly central between the pegs.

  2. Guess the front-back position of the fence, so that the router axis is positioned in front of the back plate, by about 1/2 the thickness of the disc you're grooving. Drop the cutter back down out of the way.

  3. Slide the front plate onto the pegs. drop the disc down into the gap between the two plates, so that its edge rests on the pegs. Clamp the plate so that the disc is tight enough not to wobble, but not clamped rigid (can be rotated by fingers). The point is that the disc can turn, held centrally by the copper pegs. To do the ones for the loo I needed to lubricate the MDF plates (MDF disc rubbing on MDF plates). I used graphite from a 4B soft pencil (comes off easily afterwards if you need to finish the surface).

  4. Start the router and, whilst rotating the disc with one hand, raise the cutter until it's *just* skimming a thin groove in the edge of the disk. drop the cutter down again, take the disc out and check it's central on the edge. If not adjust the setup with the router fence, and move the front plate correspondingly.

  5. Once you're confident it's cutting centrally, continue to cut, rotating the disc and raising the cutter until you get the depth of "V" you need. To get a nice finish, reverse the direction of disc rotation and rotate it until you can hear the cutter isn't chattering (so it's not cutting any more).

  6. Finally, when you've finished, stop the router and remove the disc. If you're making several identical pulleys, count the number of turns as you drop the cutter below the table again, and raise it by the same amount when you cut subsequent grooves.


I used it for thin and thicker pulleys. It worked surprisingly well on thin stock (6mm, I think), but the edges of the pulley were quite fragile. On 12mm it was brilliant - easy to set up and nice results. Mk. one eyeball was quite adequate for front-back alignment. I reckon it would produce very nice results in hardwood too, but you might need to run the router flat out, as the velocity of the pointy bit of the cutter is negligible.

Improvements:

  • I could add a captive bolt to the back plate, coming out through the front plate, with a pair of nuts clamping it, to set the distance between the two (couldn't be bothered). It would make setup quicker, but to be honest it's not exactly fiddly now.
  • Dust extraction isn't brilliant, but it's only taking a tiny amount of material away, so that hardly matters.
  • The design is inherently guarded, so much so that it's a struggle to see the cutter when making adjustments (a torch/flashlight is helpful). If you're making pulleys thick enough to get a finger in between the two plates, a different approach might be safer - needs some more thought I guess. Wearing a builders' rubber-fingerprint glove gives more than enough grip to rotate the disk against the cutter.

Anyway, construction took about 1/2 hour and was quite undemanding. You do need properly parallel pegs though, at right angles to the plates, so a properly square pillar drill to bore the holes is sensible, but it's the only tricky bit. If you Araldite the pegs in from the back, there's nothing to catch the edges of the discs on, and you can easily file the back off smooth, if you need to.

I haven't bothered with photos, because there really isn't much to look at, but I'll take some if people really think they're needed.

Hope it's useful to some budding Heath Robinson (or Thomas Crapper!) out there... :)

E.


*The venerated 'Saint Thomas of the Royal Water Closet' didn't actually invent the device, as some claim, but did make a Victorian business success of it. Nor, according to Wikipedia, is he the origin of the verb 'to Cr4p', either. Life is full of surprises. He did however design and install the poo pots into Sandringham, earning a royal warrant in the process. It was a novel use for Cedar of Lebanon (toilet seats), too.
 

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