Clamping Idea / Suggestions

[simso]

Hey folks, after some thoughts / ideas.

Customer has wanted some drums made out of solid tree trunks that he cut down many years earlier.

This one was the first one machined up.

The issue I have is how to hold it down for final machining without cracking the body.

Up until now, Ive used screws into the ends secured to a jig plate which is then secured to my cnc bed.

I need to trim the ends to final height about 4mm each side of the drum, this will remove the screw holes from the ends.

I was thinking of vacuum or double sided tape, but the amount of material in contact with the bed is minimal

Ideas....

Also need some more ideas on how to sand the inside to a final thickness, anyone got some tooling they could show that could possibly work

[J.F. Custom]

Hey Steve.

What about something like HHG either on the bottom rim or if not enough material, some HHG'd wooden brackets around the sides? All this then onto a scrap MDF base board that is then fixed to the CNC base. Should be rigid enough to machine, then easy enough to remove and clean up; reverse the drum and do the same again. If I understand you correctly.

Alternatively, what about a 'ring' machined down into a thick scrap base, the same internal and external dimensions as the drum shell that you can then slide the shell into? But not sure if this would be as rigid as the glue option without being quite deep.

Hmm, can't help with the internal final thickness. My initial thoughts are with a lathe and corresponding lathe tool, but not sure.

Hope it helps.

Jeremy.

[simso]

Cant be lathed, "End grain" imagine that going bang when you hit it with a chisel and it bites in

Glue is an idea, but my last choice.

[auscab]

I like making clamps for strange shapes with Bog / filler, Sellys Plasti-bond is my favorite brand , I always have it in stock for filling and sometimes gluing in things like loose knots. I think it's the best quality one compared to builders bog types , there is a big difference in the weight , the plasti-bond being heavier .

I do things like, get a block of wood slap an inch of bog on one side, stick it in a thin plastic bag, ex super market, and press it up against the odd shape I want to clamp just so the bog takes the odd shape , 15 minutes on a warm day and it's hard. leave it for a few hours then use it with clamps or whatever .

Four or six of these screwed to a board around the base may work .

Or build a timber tray 3 inches deep, make up a sand and cement mix , put your wood in a rubbish bin bag and sit it in the mix so it comes up around the sides two inches. Next day machine it , then break it off.

I thought there was a thread here with a picture of the internals of a drum being machined out with a router .
I'm not sure, but it may have had to do with one of Stuarts , Needsmorecowbell's threads.

[needsmorecowbel]

You are not mistaken Rob . This is a common jig I spotted online sometimes used for routing the shell thickness. It does rely heavily on the outside of the shell being fairly perfectly cylindrical otherwise you have the same issue as when you put a poorly surfaced piece of timber through the thicknesser (i.e. your shell thickness may just be all over the place)

http://www.youtube.com/watch?v=Bom9NwwM ... re=related

[simso]

Thanks guys,

Yeh dont like the idea of using a small router through the guts, Ive already cnc machined the inside to size and wish to sand to final dimension. Routers like the one shown will leave quite a substantial groove line running through the job, IMO thats a she be right mate style for your own job at home, think of the flex up and down. If I wanted too, I could cnc again to final dimension but I want to sand to final dimension for a better finish and more even thickness

Im probably going to have to find an old drum sander and pull the guts out of it and then make a jig to fit, was hoping someone may have previously visited this thought process and come up with something that I could knock off

[simso]

Wonder if I could adapt something like this

Copied this out of another thread

[Ormsby Guitars]

I know you well enough Steve, to know this thread was less about solving a problem, and more about having any old excuse for buying new machinery!

[simso]

I do have to admit, I love my toys (sorry tools)

[Nick]

Production shells are machined in a lathe then the bearing edges cut on a router table but then they have side grain (either a ply or segmented shell), it's unusual to have grain running full thickness along the drum's axis. I wonder if further down the track, unless the shell is fully sealed, the owner won't have a problem with splitting?
Anyway if it was me I'd make a dummy 'plug' with 20mm MDF that was a close fit with the ID and screw that down on your CNC table then once the shell's slid down over it, maybe 6-8 wedge-type clamps (or the quoins some guys here use) around the outside clamping against the plug. Should be as tight as a Scotsman's wallet when it's his round then. Having said that, I'd still do it in two cuts though, just to reduce the pucker factor.

[simso]

Thats actually a good idea nick, and very feasible without marking the drums exterior surface.

I might run with that one. Appreciated.

[Taffy Evans]

Hi, for sanding inside the drum, what about something like this, I used it to do the inside of some banjo shells. I made it many moons ago and occaisionly find a use for it.

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