I need an idea!

[Malibu]

I need an idea from a) someone clever, or b) someone experienced...
I've "finished" carving the back plate outside so it's time to start on the inside. I don't like Beneditto's suggestion of drilling a series of holes (I didn't like it on the outside either), and for various other reasons I don't like various other methods I could come up with (ie: chisel, scraper, plane, router, etc) so after much head scratching I came up with an idea for routing down to a thickness.

Basically, a wooden dowel fixed to the bench at a constant height guides on the outside arch contour (which is now facing down) and lifts the backplate up/down accordingly. This inside curve gets routed out by a fixed height router bit above the plate and in theory, as I move the plate forward/backward and left/right, a perfectly thicknessed backplate will be the end result (between the red lines). All movement is hand guided so I need to be REAL carefull putting the backplate in position or I'll hit the router bit.
It seems to work on the small part I've tried it on, but the big problem is holding the backplate steady and level while the router does its thing.

Does anyone have any ideas how to keep the plate steady and level, or failing that, how do you carve an inside arch? :confused:

[contrebasse]

I'm going to drill guide holes with my homemade drillpress and do it that way, using a gouge and planes.

I'm scared of routers ... one false move and you're stuffed. You only need the bit to grab ONCE and your top is ruined.

If it was easy, everyone would be doing it!

[gratay]

I reckon you got the right idea.......basically a pin router idea...
only problem being the a normal handheld router having the cumbersome base in the way making it hard to see whats going on..

I don't think you really have to worry about holding the plate in a level position so much but more so staying level to the contour of the arch....something like this picture should give you an idea.....

If you can somehow transform your router to work like a pin router ?? it would probably work .

i wouldn't think a dremel would cope to well .....maybe a dremel would if you went down in smaller increments maybe.
either way I'd probably do the last couple of mm by hand anyway

[kiwigeo]

A Dremel doesn't have the guts for this sort of job. I tried the Dremel and Stewmac rosette cutting jig. After one rosette job I dumped the Dremel and went to a full size router and a circle cutting jig...more power and a much cleaner cut. Also less problems with the Stewmac router jig adjustment screws coming loose (cost me one AAA grade top).

I agree with CB..drill the guide holes and work it by hand. By the time youve worked out how to do it with a router and built the jig you will have had time to work down a dozen back plates with planes and scrapers.

[Malibu]

Thanks for your help guys... I'll mull over it a bit more and see where I end up after that.
I like the idea of a pin router and setup in Gratay's photo is the ticket. It's basically what I've done anyway, but as already mentioned, the base gets in the way and makes it hard to see. I might toy with the idea of taking the base off because there's been a couple of other times that I wished the base wasn't there.
Benedetto's book has a line-sketch on how to drill the inside arch on the plates that made no sense to me when I first looked at it. I picked it up again last night and realised that what he had there was pretty much what I'd done with the router setup, only he'd set it up in the drill press to drill the holes. As I've said elsewhere, the book is great, but not real clear on certain parts until you actually start to do things.
I didn't give the dremel a thought, but from past experience it's a light-weight tool only. I'll use it for the inlay (:eek:) and that's about all..
Whatever option I go for, I plan on roughing it down to the last couple of mm and do the final carving with my collection of hand tools. This is, after all, a carving project...

Wow, I've just had another idea! I have the chainsaw; With a 17" bar I could get into the inside arch easily with that one!!!:D

Thanks for the ideas, I'll go take another look at my drill press..

[contrebasse]

Chainsaw? some bass luthiers use a grinder carving attachment ("lancelot"??) for roughing out the backs. But you need the guide holes. I'm going to drill holes to 12mm to start with, rough that out, then do another series of holes to 1mm from final thickness.

[Malibu]

There's a local bloke who does chainsaw carving and while it's not really my taste, he does some pretty good stuff. He gets a log and just hacks away at it with his chainsaw.
Anyway, I opted for the hole drilling method and I'm in the process of it now. Seems to be going ok and I feel better about having the cutting tip away from the piece as I re-position it for the next hole. As you said CB, one slip and it's all over with a router.

[old_picker]

Chainsaw? some bass luthiers use a grinder carving attachment ("lancelot"??) for roughing out the backs. But you need the guide holes. I'm going to drill holes to 12mm to start with, rough that out, then do another series of holes to 1mm from final thickness.

Those carving attachmrents are pretty deadly. You can get a wheel for a 4" angle grinder to do it very quickly. It has a thick profile and sort of stepped. They are very aggressive o need to be carefull, You can get em in bunnies. I use it to rough shape body contours on strats and teles. takes about a minute.

[kiwigeo]

Do yourself a favour and get yourself a decent caliper guage ( Iuse Stewmac one). Rough plane the back to bottom of drill holes and then finish the job using scrapers and the caliper. Run the caliper over the back and take spot readings and write the thickness in pencil on the back. Join up the readings of equal thickness and then interpolate intermediate values to make a contour map. Work down the high areas of the map with your scraper. This is how I work my tops and backs.

[Malibu]

I looked at roughing out bits for the dremel, but decided against it. I've seen carving wheels for angle grinders, but I've only got a 9" grinder, so I thought not a good idea either!
I relented to popular opinion and went the drill press, which turned out easier and better than I thought. Maybe just pre-carving nerves?
Anyway, it's all roughed out now, with just the final plane work to do, which I've started on today as well, but I think I've had enough work and not enough beer for today, so tomorrow it is :)

Kiwi: I looked at various thickness jigs, and even made one the same as the Benedetto book, but I'm still pondering on a thickness gauge design.
I'm nutting out an idea which will be a bit like a vernier setup. A cut down 6" rule as a marker with a 6mm thread that screws down to the surfaces of the plate. A turn wheel on the thread divided into 10ths will give accuracy to .1mm because of the 1mm pitch of 6mm threads.
What do you think?

[contrebasse]

Think: what if the pointer was a pencil and if it was spring loaded? - by passing the guage over the back at a preset depth you'd get a mark everywhere the back was oversize

[Malibu]

I like that idea... I'll incorporate that into my ponderings and see what I can come up with.
I'll have a head scratch at work tomorrow

[kiwigeo]

Malibu,

My preferred options for thickness caliper guage would be:

1. Buy one from Stewmac or LMI (I'm not on a tight budget and SWMBO realises that if Im happy in the workshop Im out of her hair).

2. Get a cheap dial caliper and mount it on a plywood jig as described in the back of Jim William's book.

Out on the job right now so cant supply you with pics of my procedure for thicknessing tops and backs.

[Paul B]

Those carving wheels for angle grinders are pretty aggresive, better off using a normal disk. I once carved a western red cedar kayak paddle with a small angle grinder with just a normal metal grinding (not cutting) disk. Not too aggresive, lots of control. I know other guys are doing the same with carved plates for guitars and mandos. You need to round over the edge of a new disk on some metal before you start on the wood tho.

I bought a new 5" grinder from bigw for $29 a couple weeks ago, came with some really crap disks that needed throwing away. A couple bucks more for some decent disks.

[Malibu]

Kiwi, it's a nice gauge at stewmac's, but woah... outta my price for now. A little bell went off in my memory though, and I rummaged around in a million boxes in the workshop and found my old dial. It's only a 5mm stroke, but I'll ponder over it tonight too. Still carving at this stage, so there's no rush :)