Making a cavity template from a sample cover? Help?

cmjohnson

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For the life of me I can't remember how to do this.

I have an electronics cavity cover and want to make the complementary template from it, so I can route the cavity recess.

I know there's a way to do it but I can't remember it and can't find the directions on how to do it.

I'm not talking about hand tracing it and making a new template by hand, it's a copy process using pattern bits in some way.

Got any ideas?
 

Murkar

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One way is to use a piece of aluminum flashing, or something stiff like that (but perhaps easier to cut). Trace your template with a knife, then pop out the middle piece. Use the aluminum (or whatever you use) as a template to then copy the template shape in MDF :)
 

dickjonesify

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^I believe that's the way. What do you mean by "1 to 1 system" Bruce?
(Not being a smartypants. I really just don't know :dunno:)

:dude:

Wait....I think I follow you now.
Still thinking about another way. :hmm:
 

bruce bennett

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^I believe that's the way. What do you mean by "1 to 1 system" Bruce?
(Not being a smartypants. I really just don't know :dunno:)

:dude:

Wait....I think I follow you now.

like the average pattern bit is a 1/2" with a 1/2" bearing so the template must be the actual size of the cavity you wish to make..

the bit system above uses a 1/4" bit and two different sized bearings on a collar to make first an under sized tracing for the positive part. then the over-sized bearing to make the inlay "hole"

I don't' like them 'cuz there's "math" involved..:D
 

cmjohnson

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Thanks. Now that you mentioned it, I remembered it.

Here's how I did it once before:

Use a 1/2" diameter guide collar and a 1/4" bit. Make a cover template made from 1/4 or 1/2" plexiglas using a pattern bit and the original cover. Now, being very careful to never let the collar leave contact with the cover template, route around the cover template into an attached blank.

You now have the outside cavity template. But it's oversized.

You now use a larger guide (and may use a larger diameter bit) with the oversized template to make a cavity that's smaller than the new template. It's late at night right now and the math portion of my brain is asleep so you'll have to figure out what combination of guide and bit diameters will yield the proper sized cavity.

This will be a dead tight cavity. You might want to adjust it to give some clearance, by using a slightly larger router bit or slightly smaller guide. Or just do some hand sanding.

CJ
 

H.E.L.Shane

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this is what i do

trace the cover on 1/2" MDF or void free plywood (mdf wont warp though)

cut out the center with a scroll saw, jig saw, or even use forstner bits

then, I tape straight edge wood scraps to the top, splitting the pencil line and use a pattern bit on the router table and rout the straights to the line.. then carefully sand in the corners on the spindle sander...

then i test fit the template with the cover to see that it fits even and loosely for paint accumulation on the guitar.. then a test cavity to prove it...

then i write "Master" on it, and make a copy and use the copy.

H.E.L. single cut guitars use commonly available control cavity covers :thumb: but the templates were made in house!!!

I have a couple other sets for other shapes..

its a bit of time to get it right maybe... but the idea with the "master" is that you only have to invest that time once
 

cmjohnson

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Success.


Here's how I did it:

Starting with a master template for the cavity cover, which is used with a flush trimming laminate bit to make covers, I attached the cover template to a piece of plexiglas with double sided tape.

I set up my router with a 1/4" helical carbide end mill and a 3/8" guide bushing, and
routed around the cover template, being careful to keep the guide bushing in full contact with the template at all times.

I routed through the new template in several passes.

This new template is wider in every direction by the diameter of the bit, 1/4 inch, plus half the additional diameter of the guide bushing, which works out to 5/16 inches. The new template is 5/16" larger on all sides.

Next, I used the same 1/4 inch router bit but switched to a 7/8" guide bushing.

I placed the new template on top of a test piece, clamped it down, and made a test cut. The resulting cavity is a super tight fit to the original cover template.

The math works out like this: The new template is 5/16" larger on any side. So it's 5/8" larger in total size.

To cut a matched cavity, the cut needs to end up 5/8" smaller than the template.

The bit is 1/4" or 2/8". Use a 7/8" diameter guide bushing and the difference is 5/8", just what we want.

When using this to cut, the bit takes 1/4 inch and there is 5/16 inch between the rim of the template and the cutting edge of the bit. There's that 5/16 inch I got between the original template and the cut edge of the new template.

So, just keep in mind that this combination works any time you want to make a cavity template from a cavity cover template. 1/4" router bit with 3/8" bushing for making the template, and 1/4" router bit with 7/8" bushing for cutting the cavity recess with that template.

The difference between the two bushings is twice the diameter of the router bit. THAT is the key measurement. As long as that holds true, you can use any combination of bit and bushing sizes that fits the formula.

I ended up with a recess that's so closely fit that I'll probably want to sand it out
a little wider. Or I will have to mask off the recess during the finishing process.
There just isn't any clearance to allow for finish thickness.

I like tightly fitting covers. This method makes them.

CJ
 

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