Transfering/ laying out holes for adapter plate.

[mac1911]

Since you said it’s similar, once the backplate had the correct locating shoulder I used a C clamp to hold it in place on the spindle , used a short round stock with a machined point to act as a transfer punch , you just need it long enough to stick out the spindle so a brass punch on an angle can give it a tap to make a small mark on the backplate . , made one mark , removed it , drilled and taped just that one , used the first finished hole to bolt the backplate on , mark the next , repeat 2 more times . There’s plenty of clearance in the spindle holes , the fit between the spindle and backplate locating shoulder is the critical dimension

On hold for the moment , still looking for a piece of stock to use.

 

[Alcap]

I used a cast iron barbell plate , was quite a challenge getting through the outer layer

 

[mac1911]

Military training for me was
measure O.D.(outside diameter)for the new plate
measure bolt hole circle diameter
measure bolt center to bolt center

use cast iron for the backing plate

find center pilot hole it
scrib bolt hole Circle
scrib bolt holes

another way
cut a paper. Pattern

I was trying to sort this out in my head and I knew there had to be a way.
I eventually found this and it looks like it will work great.

 

[RJSakowski]

Usually, a bolt hole pattern is made on some nice even number, be it Imperial or metric. I will measure from hole to hole to determine what that number is. For a three hole pattern, I measure the distance for all three combinations and average my measurements. If measuring the holes, measure from the far side of one to the near side of the next or measure near side to near side and ad the hole diameter or from far side to far side and subtract the hole diameter. My preference though is to insert tight fitting pins or in the case of threaded holes, socket head cap screws tightened to the face.

The caveat is that manufacturers of some equipment, in particular Chinese, are sometimes sloppy in their layout so their locations may not be accurate. The choice then is to either make your holes to fit the design intent or to make them to fit reality. Usually, you are pretty safe making them to design intent as there is typically some clearance slop in the fit up.

 

[mac1911]

These are representations of exact methods for patterning holes on a circle. A rotary table is the easy way to machine the part, but you can map out the cartesian coordinates of each hole and just work it out on your mill table with a drill. You can find as many digits past the decimal you need, find center, and go to town.

View attachment 438770View attachment 438767View attachment 438769View attachment 438768

Do you have links for online info for these methods

 

[pontiac428]

Do you have links for online info for these methods

Not really, I learned that stuff in math class doing what is called geometric constructions, and also in mechanical drafting classes. A lot of the old machine shop texts have chapters on layouts and dividing that cover the techniques.

Chapters 2 and 3 of this book (written in 1906) include a practical look at constructions that apply to this purpose. I've linked it from my onedrive because it's too big to attach:
20th Century Machine Shop Practice

 

[mac1911]

Not really, I learned that stuff in math class doing what is called geometric constructions, and also in mechanical drafting classes. A lot of the old machine shop texts have chapters on layouts and dividing that cover the techniques.

Chapters 2 and 3 of this book (written in 1906) include a practical look at constructions that apply to this purpose. I've linked it from my onedrive because it's too big to attach:
20th Century Machine Shop Practice

Thank you I actually like the older material. I have been looking for machinist type books locally since I grabbed a lathe year and a half ago.
I left my name with a few local small used book stores that say they come in from time to time and will call me.