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Calculating Bolt Hole Radius....?
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EEasy
Originally posted by Ken_Sheaoldtiffie
In the 2nd formula for finding the diameter for a triangle
D= Sx1.1547 = 2E
What is the = 2E
Thanks
I will explain that:
E is the diameter of the inscribed circle  the internal one that is tangent to all three sides of the triangle.
D is the diameter of the circumscribed circle  the external one one that "touches" all three "points" of the triangle.
S is the distance across the "points" of the triangle.
D is twice/double E or put another way: D = 2E or E = D/2 = 0.5D
In the equation:
D= S x 1.1547 = 2E
all three values are equal, hence the S x 1.1547 can be eliminated or disregarded when only considering the values D and 2E
I hope this helps
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oldtiffie
In the 2nd formula for finding the diameter for a triangle
D=Sx1.1547 = 2E
What is the = 2E
Thanks
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Originally posted by oldtiffieas promised, I have completed the sketches for hole spacings, centre distances and lay/setouts for equisized and equispaced holes  Sketch/sheet 1  as well as the general case  Sketch/sheet 2  where the holes may or may not be the same size or equallyspaced and may be on or off the centres or pitch circles.
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I have a set of center line gages that are very useful.
http://www.victornet.com/productimages/39.jpg
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Out of the cot
Originally Posted by Black_Moons
What does cot mean on the page http://www.cnccookbook.com/MTLayout.htm for dovetails?
In a right angle triangle the tangent ratio (TAN) of an angle (A) is the ratio of the side opposite (OPP) the angle concerned (A) to the side adjacent (ADJ) to the angle.
TAN A = OPP:ADJ = OPP/ADJ
TAN A/1 = OPP/ADJ
The cotangent ratio is TAN/1 inverted ie it is 1/TAN
For the equation to be valid, both sides of it must be inverted ie TAN A/1 inverted becomes 1/TAN A = COT A
So.
TAN A/1 = OPP/ADJ = 1/COT A
Invert all three expressions or values and we get:
1/TAN A = ADJ/OPP = COT A/1
Or put simply:
TAN A = 1/COT A
and
COT A = 1/TAN A
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For any even number of hole BC take two screws and measure across them with calipers or micrometer. Subtract the size of screw. For odd number of holes. Measure between two holes and trig it out using half the distance hole to hole for the radius. Off at work we have to do drawings out on the floor of machines that come in for service. Sometimes they will have one hole offset so it has to go together the right way. Then we have to trig it out to come up with the angle. Not surprisingly the offset is usually 5D
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What does cot mean on the page http://www.cnccookbook.com/MTLayout.htm for dovetails?
Fred
Edit: Ooops! Failed to read the responses past page one. Please ignore this post, I will! :)Last edited by Pherdie; 11222009, 11:12 PM.
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I have a DRO but there are times when you can't get the part off to lay it on the table and then you need the formulas. The formulas I have are not as easy to use as these.
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If you have a mill with a dro, you can indicate center of each hole and record the xy positions. Then you can trig things out. Sort of a poor mans cmm.
Clutch
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Thanks
Originally posted by CarldHey Tiff, after some manipulation of the size of the page of formulas I was able to get it on one page in Word and will store it and make some printed copies to use in the shop. I don't think I have ever seen a simpler set of formula to find the bolt circle dia. or sides of the circle.
Thank you very much.
I'm glad it helped.
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[quote]In my attempts at figuring out the bolt hole radius, my measurements fall between common metric and Imperial numbers so I don't know which system was used. [endquote]
Don't be supprised if they come out NEITHER. :)
I did this for the base mounting of a DeWalt router and using every
measurement (collet to shoulder screws all the way around every
combination) and converting to metric or english in rectangular or
polar coordinates, and nothing could be made to come out even.
:) So I just used the numbers as they came out and it was perfect.
Sure wish I could have ask the ME or draftsman that layed it out
what he intended. :)
...lew...
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Hey Tiff, after some manipulation of the size of the page of formulas I was able to get it on one page in Word and will store it and make some printed copies to use in the shop. I don't think I have ever seen a simpler set of formula to find the bolt circle dia. or sides of the circle.
Thank you very much.
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Setout sketches
Once again  back to the OP:
Originally posted by YankeeMetallicI frequently get chucks and backing plates from a customer in the Glass Blowing business. It seems Glass Blowers often do whatever it takes to get parts put together just to keep the machines running. There are so many bizarre compilations of components, chucks, and backing plates in that business. The Glass Blowing industry prefers to use metric increments in it's parts and accessories but that is not always the case. Each Blower also prefers their own combination of bizarre chucks, Drill Chucks, on face plates, back plates etc. for the repetative parts they specialize in.
My dilemma: HOW TO DETERMINE THE BOLT HOLE RADIUS FROM EXISTING BOLT HOLES?
I make parts to refurbish Glass Blowing Lathes (Typically Litton models). When I have to make a new back plate for instance, I have to match the 3, 4, and sometimes 5 bolt hole pattern already drilled in the chuck / plate. Since the chucks all have thru holes, I cannot use a compass to find the centerline and determine the bolthole radius to make a new backplate etc. I have a method that I use where I install screws/ hole pin gages into the threaded holes, and try to create triangle dimensions by measuring the outside of each pin, subtracting half the width of the pin to find center.
This cannot be the optimal method as there are so many variations that affect precision: metric screws, uncommon screw pitches, worn out screws that tilt in the holes when being measured, undersized or varying screws peak to peak. Often times I do not have the ability to contact the user / owner of the parts since I get the partedout work from my customer. Sometimes I get the original screws so I can determine by pitch if they are metric or Imperial, which helps in determining the closest common radius, other imes I don't get the screws that were originally used to combine the chuck to the back plate or spindle nose. I often resort to screwing taps into the tapped holes to figure out the pitch thread and therefore the screw size.
I have also used a CoAx indicator to determine the center of the hole when inserting Hole pin gages. But that only gives me the point of a triangle/ pentagon so I can make a math calculation from there.
Many glass blowers require tight tolerances. In my attempts at figuring out the bolt hole radius, my measurements fall between common metric and Imperial numbers so I don't know which system was used.
Those of you who have experience with glass blowing chucks will know where I am coming from.
I know there is an easy way, but many of my old timer machinist friends that could answer this have passed on in the last few years. I have searched the internet, this and other machinist sites but cannot find the answer.
I have a DRO with 'Bolt Hole pattern' to drill the new holes, but I cannot figure out how to use it in reverse, and it is not in the Accu Rite manual.
Obviously I have no formal machinist training, but I scratch out a living with decent machines and information from books / friends.
Thank you in advance.
as promised, I have completed the sketches for hole spacings, centre distances and lay/setouts for equisized and equispaced holes  Sketch/sheet 1  as well as the general case  Sketch/sheet 2  where the holes may or may not be the same size or equallyspaced and may be on or off the centres or pitch circles.
I hope it clarifies things somewhat and is of help:
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I don't know if it is a standard or best method, but I usually measure from hole to hole using calipers. I do both inside and outside dimensions for each pair of holes and average them for the center to center distance.
If there is an even number of holes, I measure all the opposite pairs and average the average readings for each pair. And, yes they usually do not agree from pair to pair.
If there is an odd number of holes I use equations like dickeybird posted. Again, I measure a number of pairs of holes for each distance and in the equations and average either the distances or the calculated diameters.
I use calipers because in most cases  in all the cases that I have ever measured  there is really no need for higher precision. You WILL get at least several thousanths difference between different pairs of holes. You will have to use pins or other devices if the holes are small or badly worn on the edges. Just keep the pins parallel and averaging the inside/outside measurements will take care of any difference between the pin size and hole size.Last edited by Paul Alciatore; 11222009, 01:58 AM.
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