backstrap question.

[old_picker]

Just in from stewmac is this 1/4" zipper back strap which looks real nice but seems slightly under the size of a 1/4" rout. Only a whisker mind and it slides in the slot real easy. Tried a couple good quality bits like CMT and torquata.

Any of you accoustic builders used this stuff??
When you get in some glue etc does it fits in ok without a obvuious gap??

[kiwigeo]

Ray,

If the strip is slightly undersize for a 1/4" router bit then go for a smaller bit and do a couple of passes. I usually do this even when I can find a router bit to match width of the strip. I have 1/4" shank router bits down to 1.5mm just for this purpose.

If the strip is wood and youre gluing in with water based glue then yes there will be a little bit of expansion of the strip.

Cheers Martin

[rhoads56]

Just try some in scrap first. When I've inlaid strips, especially ones made with end grain facing outwards, I've found they expand a reasonable amount, more than you may expect.

[kiwigeo]

Good advice rhoads....always do a test cut.

If swelling of the strip is a worry then use epoxy.

[old_picker]

I ordered smaller bits today. I didnt realise you could go smaller than 1/4" in a 1/4" shank bit. I found 5.5mm and 6mm from carbitool.

Good advice I will do a test piece.:2tsup:

I gave stewmac a blast which was prolly premature and just shows my ignorace bout these things. I guess I expected the wood binding to be sized even just like the plastic stuff. I told em i reckon they need to say nominal 1/4" on it.

Some of the pieces [I got 4] were way down around .22" with a huge gap you could stick an e string into.

[kiwigeo]

Ray,

Campiano and Co's book has instructions on routing for a back strip. I clamp my trusty straight edge on the back of the guitar and run the router along same. I move it a fraction at a time until the strip fits. Channel depth is usually about 1.5mm.

[old_picker]

Yup same as me with the straight edge but i am too parasnoid to shift it in case it goes off paralel or even worse off centre. I like to do them kind of cuts once only. The more times you go at it the chances of a stuffup increases exponentially. Thats why i hate trying router cuts with the dremel. Mark it out careful and hit it once with the right bit in a machine that can do the job easily with plenty power left over.

[Malibu]

I hatched an idea at work today that might work. I'll try it one day, but if anyone thinks it has potential, go for it :2tsup:

An adjustable parallelogram that sets the course width via 4 screws (one in each corner) that can be locked into place by wing-nuts or something. Use as many extra holes as you think you may need.
The center point lines up with the center line of your back strip and lock the whole assembly into position on the job.
If you set the fine adjustment by 'twisting' the two straight edge guides in, it will close the distance to the router base. A little bit of maths for base size, bit size and final channel size and it should be fairly easy to set up. If there's any fine adjustment to do, loosen the 4 adjustment points, open up the straight edges and lock it back into place... It should automaticaly keep the channel guides in parallel and allow for fine adjustment until the finished size is perfect. :)
You could make the straight edges whatever length you think is needed.

The picture is a rough sketch in autocad, but hopefully it makes my dismal description easier to understand :-