Eyeball Engineering

[STANG KILLA SS]

Z06 wheels! love 'm!

[Duuuuuuuude]

Ready for instal.

[Szczerba]

Look great, mang.

[Trubble]

Okay, I'm going to ask a question here, 'cause I don't know where else to put it.

It sounds to me like Duuuuuuude is using the Y-feed (?) on his table to set the bolt circle, and then turning the rotary table 60° at a crack to get the six holes spaced correctly. For eyeballing, that should work splendidly.


But I was checking in some exhaust flanges at work with 3 holes on a (iirc) 105mm bolt circle.
I wound up just taking a compass and drawing out a 105mm circle on paper, and just visually checking that the circle drawn was 'close' to the middle of the three holes. A caliper measurement hole-to-hole yielded even numbers, so I knew each was at the 120° they needed to be at.

However, my question is this:
Does anyone have a quick-n-dirty formula for finding out how far apart those holes should have been?

I could have just used my formula of

diameter x degrees x .01745,
or,
105 x 120° x .01745= 219.87mm. But the problem is that this length is actually measured along the circumference, not straight center-to-center of each hole.

Anybody know how to find the straight center-to-center measurement?

(and, yes, I know with the six hole patterns we typically use on wheels, you just measure to the hole straight across to find out what hole circle they're on. Just thought I'd pick some brains on how to do it with an odd number of holes.)

[monkeyracer]

Originally Posted by Trubble

Okay, I'm going to ask a question here, 'cause I don't know where else to put it.

It sounds to me like Duuuuuuude is using the Y-feed (?) on his table to set the bolt circle, and then turning the rotary table 60° at a crack to get the six holes spaced correctly. For eyeballing, that should work splendidly.


But I was checking in some exhaust flanges at work with 3 holes on a (iirc) 105mm bolt circle.
I wound up just taking a compass and drawing out a 105mm circle on paper, and just visually checking that the circle drawn was 'close' to the middle of the three holes. A caliper measurement hole-to-hole yielded even numbers, so I knew each was at the 120° they needed to be at.

However, my question is this:
Does anyone have a quick-n-dirty formula for finding out how far apart those holes should have been?

I could have just used my formula of

diameter x degrees x .01745,
or,
105 x 120° x .01745= 219.87mm. But the problem is that this length is actually measured along the circumference, not straight center-to-center of each hole.

Anybody know how to find the straight center-to-center measurement?

(and, yes, I know with the six hole patterns we typically use on wheels, you just measure to the hole straight across to find out what hole circle they're on. Just thought I'd pick some brains on how to do it with an odd number of holes.)

You would be trying to find the chord length:





The two graphics above show the different ways to find it...

so you would be looking at (diameter) * (sin (degrees/2))

For the bolt pattern you are talking about, the holes should be 90.93mm center to center.

Hope that helps!

[Duuuuuuuude]

Originally Posted by Trubble

It sounds to me like Duuuuuuude is using the Y-feed (?) on his table to set the bolt circle, and then turning the rotary table 60° at a crack to get the six holes spaced correctly. For eyeballing, that should work splendidly.

I do actually measure stuff, you know.

[Trubble]

Originally Posted by monkeyracer

You would be trying to find the chord length:


Hope that helps!

More than I can convey, thank you.

Originally Posted by Duuuuuuuude

I do actually measure stuff, you know.

Ooops. My bad, I sincerely apologize. I over-simplified the process and failed to give credit for efforts made, and for this, I am truly sorry. I have admonished myself repeatedly since reading this, and will likely continue to do so until noon on Monday. About all I can do at this point is humbly ask for your forgiveness, thank you for establishing a boundary, and letting me know I've crossed it. I promise to try and be a little less arrogant in the future.

[Duuuuuuuude]

Dilemma time. CNC conversion or a small (ish) lathe?

[rob_b]

Lathe... If I remember correctly you have a round column mill. They are typically seen as poor candidates for a conversion. Not that any of the China machines are great. But, if it would fit your space and budget consider getting a second mill down the road to convert to CNC. Preferably one with a head stock that slides on ways. I often wish there was a manual mill sitting next to my CNC'ed one. Just my .02

[SkaldidDog]

Originally Posted by rob_b

I often wish there was a manual mill sitting next to my CNC'ed one. Just my .02

There is something really convenient about an etch a sketch when you just want to knock out a simple part or mod in a few minutes. Since I don't do production I've never wanted a CNC machine. A manual knee mill would rock!...because of the need for a separate lathe. I hate moving the vice to use the tail stock and then having to re-tune the vice.

J

[monkeyracer]

Originally Posted by Duuuuuuuude

Dilemma time. CNC conversion or a small (ish) lathe?

Both!

But, maybe start with the lathe. CNC gives you some great repeatability and complex design capability, but the lathe gives you another method of creating. If you find that you still want the CNC, I'd agree with rob_b: look at some of the solid column mills with dovetail ways. I've got my eye on the Littlemachineshop mini mill and CNC conversion, and as soon as funds free up, I want to get it.

You are looking at a few hundred for a cheap small lathe, or $2k minimum for a CNC conversion on a new mini mill. (Or even almost as much to convert the rong-foo, and it may be more work than it is worth.)

[CREEPERBOB]

Originally Posted by Duuuuuuuude

Dilemma time. CNC conversion or a small (ish) lathe?

Lathe (smallish) $$$,

CNC $$$$$$$$$.................$$$$$$$$$$$$$$$$, Learn a little extra math and read, read, read, I almost have it done, $$$$$$$$$$$$$

[Etype R]

I use my CNC a lot more then I use my lathe. I even do lathe oops with it.

[BigSki]

Hands down, a lathe.

[Duuuuuuuude]

The only reason I want a lathe at this point in time would be for making wheels and various small, round parts. I could get by with a sub $1k lathe, but my concern would be not having any room to grow.

CNC is looking really good for several reasons...production being the biggest. I just wrapped up a run of 350+ individual parts. It was such a grind that I don't want to do that again for a long, long time. CNC would also help a ton with making wheels, especially if I add a 4th axis. Lathe operations would happen too.

Yes, its a round column mill, and I know the bad rap they get, but its been doing well for me. I don't have the $ to invest in a whole new setup.

[TEDROCKZ]

Way too fancy....



In all seriousness is it worth it? Cost vs gain? Would large runs like you said you done be cheaper to outsource to a mass production shop? I guess if the foreseeable future looks busy enough it would worth spending the money though. I'd vote buy a lathe first and maybe cnc later.

[JohnRobHolmes]

lathe all the way, but cnc is for sure a great benefit.



Can you mount lathe tools on your mill headstock? Could you mount a lathe drive on your mill bed?

[JohnRobHolmes]

Originally Posted by TEDROCKZ

Way too fancy....



In all seriousness is it worth it? Cost vs gain? Would large runs like you said you done be cheaper to outsource to a mass production shop? I guess if the foreseeable future looks busy enough it would worth spending the money though. I'd vote buy a lathe first and maybe cnc later.

Very good points here.

Unless you are looking at doing it as a JOB, be careful looking at it from the aspect of what work you will be able to do. I would choose based on what you want to learn more, what would be most fun for you. When you boil down the costs as a machine shop would, you have your own time per hour to pay for plus the machine shop time of $50+ an hour. It almost always ends up being cheaper to hire somebody else unless you are shortchanging yourself on the hourly costs of running a machine OR unless you are really damn fast at making parts.

[rob_b]

Originally Posted by SkaldidDog

There is something really convenient about an etch a sketch

Plus, sometimes it's just fun to rip into some material!

[Duuuuuuuude]

Originally Posted by TEDROCKZ

In all seriousness is it worth it? Cost vs gain? Would large runs like you said you done be cheaper to outsource to a mass production shop? I guess if the foreseeable future looks busy enough it would worth spending the money though. I'd vote buy a lathe first and maybe cnc later.

I reeeeeeally want a lathe, but a cnc seems more practical at the moment. With 4 different products, 2 prototypes, and a handful of wheel designs that are all done in-house, I'm constantly looking for ways to shave time on operations. It'll be worth it if I can do it reasonably.

Could I farm stuff out? Sure. However, DCW funds itself and I need the most bang for the buck to upgrade and expand. Right now that means doing everything myself in whatever time I have to do it in.