Installing drill bushings

[BillN]

I'm making a drilling jig out of 1/2" MDF and installing these:



Overall length and width of the inserts are 1/2x1/2. I'm planning to use a 1/2" forstner bit, will that be a tight enough fit?

**my 1/2" forstner bit is dull, do the serrated edge bits cut any better/smoother than a standard bit?

[daddo]

I might try a paddle bit and do a test piece, then grind the paddle bit a tad smaller if need be.
I have sized some paddle bits for such things as plugs and so on.

If it doesn't hold into the mfd, you might fit a plywood plug into the mfd with glue then drill the hole in the plug for better strength.

[Routerman]

Not in MDF. The fit is substrate sensitive.
Probably start a .498".

[BillN]

Routerman said:

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Not in MDF. The fit is substrate sensitive.
Probably start a .498".

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How?

[John Mihich]

Use them for my jigs. Just use the bit that is exactly the same as the smooth end. I have one jig I have used for hundreds of holes - holds just fine.

[BillN]

Thanks John, Last night I came up with idea of using a little thin CA glue around the insert. Maybe I'll skip that step.

[Routerman]

Best fit in any substrate = a fit whereby you don't deform the area around the bushing but is tight enough not to be pressed out.
That is, by hand or drill accident. What's it take to the do that? Money.
You need a reamer or an adjustable drill that will change diameter.
Does the jig have to stand hundreds of cycles?
Then I'd test the hole size before using up your jig substrate.
Only a few holes? Then maybe no bushing at all; just a hole that will line up the drill to the work.