Bolt Circles Help

Wug · Post by **Wug** » Mon Jan 26, 2009 12:31 am

Hi,

I'd like to put a circle of Grandt Line bolts around the face of plastic disks that are about 1.125" (28mm) in diameter. Since this is for an original design anything from 12 to 20 bolts per circle is acceptable.

I've tried laying out the pattern with protractor, compass, ruler and pencil but I'm not getting anywhere near the accuracy needed. I don't have a CAD program.

Does anyone have any tips or advice on producing nice symmetric bolt circles?

Thanks,

Mike

Andrew Gorman · Post by **Andrew Gorman** » Mon Jan 26, 2009 12:36 am

If 12 will work, print out a bunch of appropriately sized clock faces and use them to mark the locations. Just a suggestion!

Chacal · Post by **Chacal** » Mon Jan 26, 2009 9:30 am

With drawing tools it is easy to divide an angle in 2, and it is equally easy to draw a line perpendicular to another (you need only a compass to do both).

So, draw a diameter, draw a perpendicular to that, [you have 4 quadrants now] divide each of them in two [8 angles], then again [16]. The good thing is that you only need to divide two of the four original quadrants (the diametrally opposed ones will be automatically divided), four of your 1/8s and 8 of your 1/16s.

In the end you'll have 16 divisions.

tetsujin · Post by **tetsujin** » Mon Jan 26, 2009 12:57 pm

I would do this by creating a guide.

One way to create a very precise guide would be to design the part on the computer and then photo-etch it.

Barring that, another way to create the guide would be to drill it on a drill press: cut a circle of plastic, pin it down at the center so that it can turn, and drill the first hole at the edge of the circle... Then you need a guilde that keeps the spacing between holes consistent: turn the circle by a certain increment, and then rig up something so that after you drill the next hole, you can turn the disc and get that next hole to the same point.

Of course, with the second method there's bound to be some issue with the end of the circle: probably the spacing will be noticeably off when you get to the very last hole. The way I would deal with that is by distributing the error around the whole circle: lay out four or eight bolts on the guide using protractor and ruler, then use the spacing guide to get all the points in-between. That way there will be more (four or eight, instead of one) areas on the circle with a relatively large error, but the error itself will be smaller (1/4 or 1/8) than what you'd get by incrementally going around the full circumference.

And I don't expect I'd get a satisfactory result the first time with this method, either. Most likely I'd have to make a couple attempts. Getting precision is frustrating sometimes...

Joseph Osborn · Post by **Joseph Osborn** » Mon Jan 26, 2009 2:15 pm

I recommend you download Inkscape (www.inkscape.org), which is an open source (free) vector graphics program, to draw templates for your pattern. I like to print templates onto label paper and stick the template to my plastic card. Use a scriber to make tick marks through the label into the card, and then you have your bolt locations ready to go. If you drill the marks with a small bit, then you just drop the Grandt bolts into the holes.

Wug · Post by **Wug** » Tue Jan 27, 2009 3:28 am

Thanks Everybody,

I think part of my problem was trying to lay out the pattern with a pencil. The line was too thick and it wasn't straight enough.

I'll try scribing the pattern on a piece of sheet plastic then use dividers to tweak the spacing before I drill holes.

I'm also downloading (on a very slow connection) Inkscape.

Does anyone have additional advice?

Thanks again,

Mike

Chacal · Post by **Chacal** » Tue Jan 27, 2009 11:10 am

If the disks are already cut, and you have to mark them:

1. buff them with steel wool so they can accept a good pencil line;

2. use mechanical pencils (for precision work I like 0.3mm, but 0.5mm is fine);

3. use hard lead (2H minimum. If you can find 3H or 4H, go for it) for both the mechanical pencil and the compass;

4. keep the compass lead properly shaped and positioned (the lead should be sanded at an angle—like this);

5. give yourself more room: take a sheet of plastic, cardboard or whatever as thick as the discs and punch a hole slightly larger the the disk diameter. Plop the disk in there and you can lay rulers and triangles flat to draw properly;

6. use a good compass, one with a thumbwheel to adjust the opening.

NNYGamer · Post by **NNYGamer** » Tue Jan 27, 2009 11:16 am

One other trick might be to use a small gear, count the teeth and mark in between the ones you want for the right amount of bolts

Wug · Post by **Wug** » Wed Jan 28, 2009 2:37 am

Thanks Chacal and NNYGamer,

I'll try laying out a template on sheet styrene after I replace the door switch clip on my clothes dryer.

I've thought about building a little dividing head out of gears. But little plastic gears probably have too much play and I'm not sure I could build the dividing head straight enough. Also, I'm not sure if any of the gears lying around the house have the right number of teeth.

Thanks,

Mike

srspicer · Post by **srspicer** » Sat Feb 07, 2009 10:50 am

OK wug,

If you want to be accurate, purchase these tools that I have, they will make life easier, and they are not expensive.
This page, if it works as a link, will show you a indexing tool for dividing circles. All you would need is a pointer on a base or a hieght guage and you can have an accurate bolt hole pattern.
http://www1.mscdirect.com/CGI/NNSRIT?PM ... O=58005446
If the kink does not work, just type in MSCdirect.com and indexing tools. If you are interested and you can't find the tool, jsut contact me and I will send you the info. Good luck.

Regards,

Scott

Mr. Badwrench · Post by **Mr. Badwrench** » Sun Feb 08, 2009 3:04 am

The indexing head that srspicer shows uses 5C collets, (typical lathe collets). To use this you will need some way to center the part on the indexer. 1.125 inches in diameter is about the top end for 5C collets, although you can get oversize collets too. It might be better to chuck a steel or aluminum plate with a half inch mandrel into a half inch collet, and tape your disc to this. It turns the indexer into a sort of rotary table, but doesn't cost as much. Still, it is more than a hundred bucks just to get started, although once you have it you can use it for all sorts of projects.

srspicer · Post by **srspicer** » Sun Feb 08, 2009 8:47 am

Mr. B is right, I forgot about the collets, but you only need the import selection of collets to give you what you need, or you can buy just a couple.
If you use the 1/4" collet, you won't need aluminum or steel plates.
Take a 1/4" dowel or styrene tube or rod and super glue it to a thick piece of plastic, using a square edge to keep the rod perpendicular to the plate. Place the assembly in the collet, when it is in the indexer. Use you hieght guage, you really should get one, to find center. Lightly weld or glue you material for your bolt plate. Use your caculator to divide 360 by how many holes you want. Use the indexer to space you holes.
I would be glad to email you exactly how I do this. It is not complicated, and once you have a height guage, you will see a whole new world of model making open up to you!

Pm me with questions, I would love to help in any way! Bolt holes are a pain!

Scott

1138thx · Post by **1138thx** » Tue Feb 10, 2009 5:59 pm

I can cut them for you on a CNC if you like. You just pay the postage.

Let me know. Its the most accurate.

Wug · Post by **Wug** » Tue Feb 10, 2009 8:56 pm

Thanks Everyone,

I can't afford to buy anything to make a couple of model parts.

Inkscape almost worked but it isn't accurate enough and it frequently locks up.

Now, I'm looking for a free CAD program that supports circular arrays.

Thanks for the generous offer 1138thx. If I can print templates I should be okay.

Mike

Kylwell · Post by **Kylwell** » Wed Feb 11, 2009 12:31 am

Uhm, if you need I can run a set out in Illustrator. Give you a pdf to print.

The way I've done something like this in the past is to print out the guide, glue it down (white glue works fine, and a little water removes the paper) and then use a tiny bit and drill as exact to the center of the X as possible, then work my way up to a proper size.

Wug · Post by **Wug** » Wed Feb 11, 2009 9:22 pm

Thanks Kylwell,

I'll give CADStd a try. I'd like to be able to create my own templates.

Mike

Wug · Post by **Wug** » Wed Feb 18, 2009 7:57 am

Thanks Everybody,

I drew templates with CadStd, glued them down and drilled the holes. It turned out okay.

Mike