layout question - bolt hole pattern

snipped-for-privacy@hotmail.com wrote in news:1128260520.193820.206700 @g14g2000cwa.googlegroups.com:

Trigonometry.

Start by drawing a triangle with the center of your three holes as the corners. Next draw two lines on each side of the triangle in such a way that the triangle becomes a square. One of those lines is the amount you need to move the table cross ways (X), the other is how far you move toward an away from yourself (Y).

To solve for the sides of the right triangle you've just drawn:

Known - The hypoteneuse is 3.607" (side c)

Angle A = 30 degrees (the original triange has 180 degrees divided by three equals 60 degrees in each corner. Since you made the new triangle a right angle to the bottom of the original triangle you take 90 degrees minus 60 degrees and you have 30)

So now you know A and c. to solve for a and b:

a=c X sin A

b=c X cos A

a=1.8035

b=3.1238

If I did the math right.

Hi Ron,

To some extent I'm figuring this out as I go along, so if anyone can think of a better method, please say.

I'm assuming you have the round, flanged component ready made. You'd be better off holding the component in a three or four jaw chuck clamped to the mill table rather than a vice. I'm also assuming you have a DRO on your mill, but if you don't it just requires a little extra mental arithmetic.

Once you have the component clamped to the table, you need to centre it under the spindle. Get one of those adaptors which enable you to fix a dial test indicator to the spindle. Bring the test indicator into contact with the component and slowly turn the spindle. Adjust the position of the table until the reading on the indicator doesn't change. The centre of your round component is now directly under the spindle. Make this position the origin (0.000, 0.000) on your DRO.

Now you need to find the radius, r, at which you will drill the holes:

r = 3.607/(2*sin60) = 2.083"

The first hole may be drilled at (0.000, -2.083).

The other holes will then be positioned at (-r*sin60, r*cos60) and (r*sin60, r*cos60). Evaluating these gives (-1.804, 1.042) and (1.804,

1.042).

If you don't have a chuck which can be clamped to the mill table, and you're making the component from scratch, you could start with a rectangular block of material, drill the holes (including a central hole to align the shaft), then cut out a rough circle and turn it to size on a lathe. But this presents its own problems.

I also doubt your hole positions need to be accurate to 0.001". Crude as it sounds, you might get away with marking the positions using a scriber and centre punch, then lining up the drill by eye.

Hope this helps,

Chris

D Murphy wrote in news:Xns96E3623603C5FBW12BU20MU38SY@130.133.1.4:

I should add that you need to find the center of you work piece, then move the table toward you 1.5619 for the first hole. Then move the table

1.8035 to the right and 3.1238 away from you for the second. For the third move the table to the left 3.607"

But I would wait until someone else comes along and checks the math. I haven't had enough coffee yet.

AutoCAD check: If the center of your bolt circle is the origin of coordinates, the holes will be at:

X Y 1.804 0

-0.902 1.562

-0.902 -1.562

No trig needed on this one...

I assume an equilateral triangle... the holes at each point at 12:00,

4:00 and 8:00. Based in the center of the bolt hole pattern, I first calculated the triangle for the 4:00 hole by drawing a triangle with the hypotenuse as the line from the hole to the center. It's a classic 30-60-90. We know the X value is 1/2 the hole to hole distance (3.607 / 2 = 1.8035). Divide that by sqtr(3) gives the Y coordinate. The 8:00 hole has the same Y and negative X coordinate. For the 12:00 hole, I make another triangle with the hypotenuse from the 4:00 hole to the 12:00 hole. Another 30-60-90 where the height is 1.8035 time sqrt(3) and then we subtract out the Y of the other holes to get the Y off center.

So, the coordinates based on center are...

0, 2.0825

-1.8035, -1.04125

+1.8035, -1.04125

-Bruce

Hey rbce,

A center-to-center of bolt-hole to bolt-hole of 3.607 will have a hub center with a radius or 2.0825. Assuming that this hub center is located at X=0, Y=0, and assuming that to start one of the bolt holes is on a line drawn perpendicular to the X0 position, then the three bolt holes will be at:

#1 X 0 Y 2.0825

#2 X -1.8035 Y -1.0413

#3 X 1.8035 Y -1.0413

If you want to start one of the bolt holes at X0, Y0, then it would be:

#1 X 0 Y 0

#2 X -1.8035 Y -3.1238

#3 X 1.8035 Y -3.1238

If you have a specific in mind as to lay-out, let us know what it is, and we'll get applicable's.

Take care.

Brian Lawson, Bothwell, Ontario.

Oops, that's trig! Still works though...

Jim

OK, what I should have said was... no trigonometric functions used.

-Bruno

jim rozen wrote:

This is what a shop computer is for.......... Check here for a bunch of indispensable little programs that keep you from frying your brain:

Tom

Oops. Bruce is right. I use a bolt circle of 3.607 dia rather than center-to-center distance of 3.607.

Try this Program out might be the easy answer

Thanks to everyone who helped me on and off the list. I will try to wrap this old farts brain around the math... been awhile since I used that calculator! If anyone can quickly crunch the numbers on my second project which uses a 1.469 bolt center to center distance that would be terrific. I am trying to learn, just takes a bit sometimes. You can lay out the x-y co-ordinates such as several did, including either way that Brian Lawson provided the data. Thank you again, this is a truely great group of minds, ron

Assuming you're still doing a three hole pattern, the following are based on 0,0 being the center point of the pattern.

X = 0, Y = .8481 X = -.7345 Y= -.4241 X = +.7345 Y= -.4241

Someone will verify my math, I'm sure.

-Bruno

snipped-for-privacy@hotmail.com wrote:

Thanks again, that has my projects rolling.

Alot of the programs, BOLTCIRC & the latest one that Micheal Allard brought to attention are wonderful if the bolt circle radius is known, but unless I am missing something critical here, when you only have the center to center dimensions for the layout, then you are back to doing the math by hand, or using an AUTOCAD type program. Is that statement correct? thanks again all, ron

The center-to-center distance is referred to as the 'chord'. If that's known, then calculate the 'angle' between adjacent bolt holes as:

angle = 360 / (number of bolt holes)

Then the bolt circle radius is given by:

radius=0.5*chord/sin(0.5*angle)

Regards, Marv

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