Hole template query

[g1_lo]

Hi, I am after a bit of confirmation on a template I want to make for some circular holes.
Basically I want to make a template to router some solid surface.

Now I am getting my local cnc guy to cut the holes for the template but I need some clarification that the size of the holes is going to produce the required dimensions.

So I've got a 30mm guide and using a 12.7mm double flute straight cutting bit.
Now one of the holes is to be a finished size of 52mm.
So I've used the formula (guide - bit size) / 2 = additional measure.
(30 - 12.7) / 2 = 9mm rounded
52 + 9 = 61mm template size hole to produce a 52mm hole?

Any help on this would be appreciated.

 

[rmwarren]

Hi g1_lo - welcome to the FOG.

There is a thread with some info on your question here:

http://festoolownersgroup.com/other-tool-reviews/ujk-technology-guide-bush-set-and-axminster-hole-template/msg277420/#msg277420

The formula we came up with was D = T-((G-C)/2) when:

T = template hole diameter
G = guide bushing diameter
C = cutter diameter
D = Finished hole diameter

I still don't have the template or guide bushing so I have not been able to field verify this but I believe it is correct. There is also a link to a PDF chart giving common hole/bushing combinations.

Hope this helps.

RMW

 

[semenza]

Hi,

 Welcome to the FOG!  [smile]

 I got a template diameter of 60.65mm using different math / formula than Richard's. I get the same from his formula. Which with your rounding up is the 61mm you have. So that makes three with the same result.

Seth

 

[jonny round boy]

That formula works for offsetting a line, but for a circle you need to double the offset (or not divide it by 2 in the first place).

So, to get a 52mm hole, you need 52+(30-12.7) = 69.3mm template size.

 

[jonny round boy]

Here you go, a visual to show it:

[attachimg=1]

 

[semenza]

Hmmmm, oh, yup.    Strike my previous post.  Good thing you checked g1_lo  [thumbs up]

Seth

 

[g1_lo]

Thanks for the quick response guys.

I think I have to agree with @Johnnyroundboy. As I was half wondering at the time of my post that no offset was needed at all, for it being a circle.

Thanks for the image also clarified the whole thing very easily.

I'll adjust my measurements for the cnc guys tomorrow and report back when the templates done.

 

[rmwarren]

Uh-oh...

So it appears that my chart is, uhmn, totally wrong. Oops.

Thanks JRB - working on fixing it.

RMW