Drilling large hole over small hole or vice-versa

[MrFixIt]

Hi

What a Cool idea Zen! I supposed if one could use a 3D square block one could get 12 uses.

Surely a circular sacrificial plate would provide many more "positions" before needing replacement?

Obviously it would need to be offset

[BobL]

Hi

Surely a circular sacrificial plate would provide many more "positions" before needing replacement?

Obviously it would need to be offset

I depends on the size of the bits you use.

A 3" radius plate can provide 6 x 2" diameter positions along a circle offset by or with a radius of 2".
For added safety you could add a 1/2" margin to the outside. With two sides than gives you 12 positions. Of course this is not necessarily how it would be used because using smaller bits you don't always need 2" worth of position and you could easily work in between the motional 2" positions. There are at least 24 1/2" segments along the 2" radius circle.

If you could readily change the offset there would be even more small positions.

I vote this idea better than the cube, maybe even tip of the day.

Cheers

[zenwood]

I vote this idea better than the cube, maybe even tip of the day.

I agree: excellent piece of lateral thinking!

Let's see, if we want an insert capable of drilling N holes in it without overlap, then the angular separation d_th between hole centres will be 360/N degrees. With a little trigonometry, the radius of the disc that closely packs N holes around a circle is r = sqrt(L/(1 - cos(d_th))) + r_drill, where L = (2 r_drill)^2/2 and r_drill is the radius of the drill bit. The figure shows some examples. A disc of 19 mm radius will be able to fit 8 10mm holes, and a disc of 44 mm radius will be able to fit 24 10 mm holes (on one side of the disc).

[MrFixIt]

Hi

I agree: excellent piece of lateral thinking!

Let's see, if we want an insert capable of drilling N holes in it without overlap, then the angular separation d_th between hole centres will be 360/N degrees. With a little trigonometry, the radius of the disc that closely packs N holes around a circle is r = sqrt(L/(1 - cos(d_th))) + r_drill, where L = (2 r_drill)^2/2 and r_drill in the radius of the drill bit. The figure shows some examples. A disc of 19 mm radius will be able to fit 8 10mm holes, and a disc of 44 mm radius will be able to fit 24 10 mm holes (on one side of the disc).

Thank you for the "vote"

Zen, I tried get your formulas to work in an Excel SS, but it does not calculate the correct disc radius. How did you do your calcs, with a CAD program?

[MrFixIt]

I depends on the size of the bits you use.

A 3" radius plate can provide 6 x 2" diameter positions along a circle offset by or with a radius of 2".
For added safety you could add a 1/2" margin to the outside. With two sides than gives you 12 positions. Of course this is not necessarily how it would be used because using smaller bits you don't always need 2" worth of position and you could easily work in between the motional 2" positions. There are at least 24 1/2" segments along the 2" radius circle.

If you could readily change the offset there would be even more small positions.

I vote this idea better than the cube, maybe even tip of the day.

Cheers

Thanks for the vote

Well how about this, set the disc of desired size INSIDE a rectangle that is offset.

So flipping the rectangle will reposition the offset of the sacrificial disc thus changing the radius used for the holes drilled.

ooooh, lots and lots of holes per disc

[zenwood]

Well how about this, set the disc of desired size INSIDE a rectangle that is offset.

Would it be more efficient to set the disc inside a rectangle or set a rectangle inside a disc? Or perhaps set the disc inside another disc?

At this point, we are close to the solution that I actually use, which is to use a piece of scrap under the workpiece that can be freely rotated or translated (because it's not an insert). Assuming the piece is rectangular, the number of holes of a given size that can be drilled without overlap is a surprisingly complex problem.

I did the calculations in Matlab. The attached Excel file reproduces them.

I looked at your Excel file: it may be that you are not doing the cosine calculations in degrees. Either (1) substitute 2pi/N for 360/N, (2) convert the degrees to radians by multiplying by pi/180, or (3) there may be a setting in Excel to interpret angles in degrees.

[BobL]

At this point, we are close to the solution that I actually use, which is to use a piece of scrap under the workpiece that can be freely rotated or translated (because it's not an insert).

My whole wooden DP table (which I don't use all that often) is clamped onto a two way cross-slider vice. When I want a clean spot I just use the cross slider to move the whole table to a fresh spot. I have an area of 8" x 8" to play with. I suppose I should make an insert for it - someday.

BTW we give that packing problem as a practical exercise to our students to do in 3D.

[MrFixIt]

Would it be more efficient to set the disc inside a rectangle or set a rectangle inside a disc? Or perhaps set the disc inside another disc?

At this point, we are close to the solution that I actually use, which is to use a piece of scrap under the workpiece that can be freely rotated or translated (because it's not an insert).

HA ha ha, that what I use too

Assuming the piece is rectangular, the number of holes of a given size that can be drilled without overlap is a surprisingly complex problem.

I did the calculations in Matlab. The attached Excel file reproduces them.

I looked at your Excel file: it may be that you are not doing the cosine calculations in degrees. Either (1) substitute 2pi/N for 360/N, (2) convert the degrees to radians by multiplying by pi/180, or (3) there may be a setting in Excel to interpret angles in degrees.

Too much math My maths knowledge was pushed out of my brain cells a long time ago and was replaced with more useful info

Thanks for the excel file.

[ozwinner]

Whoa dudes way too heavy, you lot need a hobby, try woodworking I hear its good...

Al

[niki]

HotChips

I reloaded the pictures

Sorry for the inconvenience

niki

[jow104]

well done niki (devonwoody)

[niki]

Thank you DW

Best Regards
niki

[Caliban]

Ok Guys
This is what I did.
Original square sacrificial plate, now has circular plate inside. The whole lot will slide forward to new position. I can change the size of the spacers to move the plate forward or back.
I'm happy.
Thanks for all the advice, especially Niki

[JDarvall]

But, I had a problem, sometimes I had to enlarge the 6 mm hole to 8 or 10 mm and had to drill a larger hole for the bolt head, washer or T-nut.

Another problem was that the drill length was different and to change the drill, I had to lower the Drill Press table and come back to the center of the hole.

I think what you've done there is clever.....

What I normally do to avoid these problems of enlarging holes by just a few mill is just ensure I have major jumps in diameter.

ie. pilot hole. uno. Clamp up and drill through all matching pieces with say a 2mm bit.....then, because that holes so small, you can jump to your largest hole for countersink ( or whatever) then shank diameter after etc. with each bit finding centre for you, riding on that pilot.

Do you find your method more accurate ? ... Have you found that occationally you can't pilot first ?