Bubble Cap Slot Cutting Jig

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Bubble Cap Slot Cutting Jig

Postby Lesgold » Tue May 19, 2020 8:50 pm

Been thinking about bubble caps and cutting slots lately. It’s a bit of a worry when you start thinking of dumb stuff like that before you go to sleep at night. Maybe I just need a life. Anyway, I read a lot and looked at photos of techniques and equipment used to perform this task and that got me started with some of the gear that I have in my own workshop. I have a wood turning lathe with an indexing head and quickly came up with a jig that would allow me to cut 24 perfectly spaced slots. It worked a treat but unfortunately, 24 slots was not a number that would work with either 2” or 1” bubble caps. Part of that jig that would come in handy was the method I used to secure the angle grinder. I simply cramped the guard of the grinder to a piece of plywood. I’ve used this rough technique before for holding items in place, so I know it works. The photos explain everything.
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It is quite easy to slide the grinder forward or backwards on the plywood base by simply loosening the locking screws. As you can see, no measurements were made. Just 4 blocks cut quickly and drilled before being attached to the ply base. The only critical dimension is the thickness of the locking blocks. They must be slightly thinner than the guard of the angle grinder.

Another piece of ply was cut to support the cap. Two parallel strips were positioned so that the height of the tube could be raised or lowered. This enabled the disc to be positioned at approximately centre height. A fence was nailed in place and a stop was tack nailed to the strips to position the cap.
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A clout was placed on the jig as a guide for cuts.
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Slot placement guide paper (made from 5mm grid paper) is then glued to the cap.
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The cap can then be positioned into the jig.
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The jig is cramped to the workbench and the angle grinder is adjusted to the required slot length.
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Each mark is moved to the head of the clout and held in place while the grinder slides against the fence and cuts the slot.
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The paper is removed and the slots are revealed.
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As this was just a test, I rushed and didn’t take a lot of care with alignment. It still seemed to give reasonable results. The grinder was very secure and was easy to slide to form the slit. Fingers were not near the cutting disc and I felt confident in the whole process. 1” caps could be a little more challenging however. From a safety perspective it may be better to modify the jig slightly so that the caps could be cramped at each location rather than risking fingers.
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Re: Bubble Cap Slot Cutting Jig

Postby Dunnonuthin » Tue May 19, 2020 9:24 pm

Nice little jig there Les. Nice straight slots at the same depth. Wouldn’t take a lot of effort to make either. You’d have to really cock something up to cut your fingers using that. Is the idea to cut one side at time, or slide the cap all the way past the cutting disk and do two slots in one pass?
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Re: Bubble Cap Slot Cutting Jig

Postby Lesgold » Tue May 19, 2020 9:53 pm

Thanks mate. Only cuts one slot at a time. You could make it so that two slots could be cut in one pass but that would require the cutting disc to be perfectly set to centre height. That jig took 15 minutes to knock up. The extra construction and testing time would not be worth the effort.
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equipment: Pure Distilling reflux and pot. 2” modular CCVM/ 1150mm column, 50l boiler with 2x 2400w elements.

Re: Bubble Cap Slot Cutting Jig

Postby Bobsyauncle » Wed May 20, 2020 10:27 am

Nice jig mate, cuts the slots well. :handgestures-thumbupleft:
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Re: Bubble Cap Slot Cutting Jig

Postby db1979 » Sat May 23, 2020 9:49 pm

Nice jig mate, I did mine with a hacksaw on my 2" bubbler with 1" caps (my 4" is seive plates). I think I used a dremel for some too but I wanted to keep the noise down as I was in a unit complex so the hack saw was the go-to. The hack saw really does rip through it quickly, two slots at a time too. And a good arm workout
Last edited by db1979 on Sat May 23, 2020 9:53 pm, edited 2 times in total.
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Re: Bubble Cap Slot Cutting Jig

Postby woodduck » Mon May 25, 2020 9:30 pm

nice one :handgestures-thumbupleft:
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