How to layout holes on an 8" diameter plate

tjb said:
Quick PS: Obviously, you'll need to start somewhere. I can't visualize any way to mount an 8" piece of round stock on a 4" rotary table without first drilling a set of four holes that will line up with the t-slots. Maybe use a compass to lay out a circle (at 3" according to your original post?); then mill those holes first so you can at least mount it to the RT. Then proceed according to whatever pattern suits your objective.

I would suspect your FIRST measurement with a compass should be at @8" to make sure you're at or near centered. Then you're more likely to be where you want to be on the 3" circle.

Regards,
Terry
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Thanks, I was already thinking that I would mount the plate to the table and then use it to drill the holes. My thought was to find the center of the plate set the dro to 0,0. Then drill and countersink the mounting holes for the rotary table 1.5" in the X Y directions. I have a plan in my head. I just need to work out the fine details before I drill the first hole.
 
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First make something to locate the plate radially with the RT center to get the plate centered, and only then begin with locating it in clock position. The hole in the center of the RT is your friend...
 
After being constrained radially, the plate can then be held down to the RT with flat socket head screws and t-nuts. Also have at least one locating pin to locate the plate accurately and repeatably in clock position.
 
bigblock61 said:
Thanks, I was already thinking that I would mount the plate to the table and then use it to drill the holes. My thought was to find the center of the plate set the dro to 0,0. Then drill and countersink the mounting holes for the rotary table 1.5" in the X Y directions. I have a plan in my head. I just need to work out the fine details before I drill the first hole.
Click to expand...
That's exactly the way I would approach it. Just be careful to make sure you're as close to center as possible before you drill anything.

Ditto, Bob.

Regards,
Terry
 
I would just center the RT then mount the plate to the 4” RT. Use the RT to then drill your pattern holes. I too wouldn’t go overboard on drilling the holes just yet. Drill enough for the current project and maybe a few more which would expand capabilities. You can always drill more at a later date.
 
homebrewed said:
Some time back I wrote up a little spreadsheet for calculating bolt circles. It's attached. DROs would be a handy thing to have for this kind of business, but not absolutely necessary.
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I downloaded the spreadsheet and was playing with it.
Thank you for posting it.
I have a question. When I enter a "First Hole Angular Offset" value, the table changes appropriately but the "Sanity Check" chart does not.
I tried the "Calculate Now" button but no change. Can the chart be made to agree with the table data or is this an Excel anomaly?
 
Make your layout on paper. Once you have a satisfactory layout all you need is the radius of the bolt circle and the degree spacing between holes. Dial in the degrees with the RT and the radius with either the X or the Y feed. Spot drill the holes with the plate on the RT. Remove the plate, clamp it down on parallels and drill & tap the spotted locationc.

For quick alignment of plate to RT I used fixture keys. 3 are all that are needed. Pins can substitute for key. Flat head SHCS and T nuts were used to hold the table in place.
 
Illinoyance said:
Make your layout on paper. Once you have a satisfactory layout all you need is the radius of the bolt circle and the degree spacing between holes. Dial in the degrees with the RT and the radius with either the X or the Y feed. Spot drill the holes with the plate on the RT. Remove the plate, clamp it down on parallels and drill & tap the spotted locationc.

For quick alignment of plate to RT I used fixture keys. 3 are all that are needed. Pins can substitute for key. Flat head SHCS and T nuts were used to hold the table in place.
Click to expand...

You and I think alike. I'm sitting here with autocad drawing it up now and adjusting as needed.
 
IMHO the holes are for clamping and don't need to be super accurate. In a lathe or with dividers layout your BC. Use a center head to layout 0 and 180 if the pattern is even numbered. Use your dividers to layout the bolt hole, you should be able to get the chord length from Machinery's Handbook
 
If you adr doing the layout in CAD you might consider dialing in holes with X and Y coordinates.
 
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