What’s the best way to determine/measure a bolt circle?

[Grumpy1SG]

Had a similar project several years ago, I think I know what you’re asking. While it was set up in the lathe (I knew the diameter of the bolt pattern of the clutch) so scribed it. Fortunately it was a symmetrical bolt pattern, so I used the diameter as the hypotenuse (45,45,90 triangle) calculated the length of the 2 equal sides and set a protractor. A quick leap frog around the perimeter confirmed the setting was correct ( ended on the starting point), so scripted/punched them in went to drilling/ tapping.

 

[Janderso]

Good luck and have fun Jeff ! Get yourself a Hartford Super Spacer if you ever see one around . Makes quick work of those jobs .

Hartford super spacer. Got it.

 

[Janderso]

Had a similar project several years ago, I think I know what you’re asking. While it was set up in the lathe (I knew the diameter of the bolt pattern of the clutch) so scribed it. Fortunately it was a symmetrical bolt pattern, so I used the diameter as the hypotenuse (45,45,90 triangle) calculated the length of the 2 equal sides and set a protractor. A quick leap frog around the perimeter confirmed the setting was correct ( ended on the starting point), so scripted/punched them in went to drilling/ tapping.

Whoa, that’s a good idea

 

[tq60]

More on this,

If in the lathe, and you know the diameter, simply ink up the general area and while it is turning, touch the tool.

Measure diameter and adjust cross slide as needed.

Repeat until you can get exact diameter.

On your mating part or sample, use a caliper to measure from same edge between two adjacent holes, tis should be distance between centers.

Use the inside probes as scribes, start at some place in the circle, cross scratch ND work around til you get back.

Adjust length and repeat until it comes out even.

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[Asm109]

On a flywheel, the bolt pattern might not be equally spaced. one bolt may be off so the flywheel clocks only one way on the engine.
Ford small block for sure, because they are externally ballanced.

 

[MrWhoopee]

Hartford super spacer. Got it.

Yuasa makes a good one too. Almost any little job can justify another big expenditure.

 

[tq60]

Better if you had a rotary table.

On the mill you just need to hit one hole.

You scribe the ring while in the lathe, put it on the rotary and align the drill to the line.

The table will create the pattern.

We did similar with a BBQ project, needed to make an adaptor for the brake drum hub, used a 1.25 disk from the scrap yard, did the lathe work then scribed a line.

We used a hole saw to cut a slug out so same action on some scrap plywood to make test units.

Drilled all the holes then had an end mill of correct size, used it to clean up all of the holes.

Fit perfect.

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[Inferno]

I would have done it without the pins.

Take inside diameter of hole and zero out the caliper.
Use inside dimension part of the caliper to measure the hole spacing going to both holes outside diameter.

Easy peasy.

 

[akjeff]

I need to finish this project.
A customer asked me to machine this flywheel front and back to fit for the engine conversion while expanding the pilot hole as well.

The lathe work is done, now I need to drill for this bolt circle.

So, once I determine the bolt circle I can move to my mill, center it on 1x2x3 blocks, clamp and set up the DRO for the coordinates.

Thank you for your help.

OK I'll ask the obvious.....does your mill DRO have a bolt circle function? It's an even number of holes, so the holes opposite one another are the diameter of the bolt pattern. Snug fitting pins, and measure the distance between the outside of the pins and subtract the diameter of one of the pins= bolt circle diameter. Of course this is all out the window if the bolt holes aren't equally spaced( but this can be checked by pinning and measuring adjacent holes pair by pair to confirm they're equal ), or you happen to have a DRO that doesn't do bolt circles!

 

[Firstram]

Better if you had a rotary table.

On the mill you just need to hit one hole.

You scribe the ring while in the lathe, put it on the rotary and align the drill to the line.

The table will create the pattern.

We did similar with a BBQ project, needed to make an adaptor for the brake drum hub, used a 1.25 disk from the scrap yard, did the lathe work then scribed a line.

We used a hole saw to cut a slug out so same action on some scrap plywood to make test units.

Drilled all the holes then had an end mill of correct size, used it to clean up all of the holes.

Fit perfect.

Sent from my SM-G781V using Tapatalk

Where are your shoelaces? That would drive me nuts!