Author Topic: Circular hole pattern help (Read 8665 times)

rleete · « **on:** August 12, 2012, 06:21:37 PM »

I have a cylinder head that I'm trying to make a hole pattern in, to bolt to the cylinder. It's about 1.5" diameter, and roughly 3/16" thick. I've tried both laying out the holes with a compass and making a groove using the lathe for the bolt circle.

In either case, when I transfer the part to the mill, and try using coordinates to locate the holes, I end up with at least one hole that looks off. Not by much, but enough that it's visible, and it bugs me. Since the holes are so small, even a couple thou off is apparent, making the part look lopsided.

So, how do I get a circular pattern of holes to be even and concentric?

b.lindsey · « **Reply #1 on:** August 12, 2012, 06:48:37 PM »

Are you adjusting for backlash on both the x and y axes? That could throw you off a little. Do you have a rotary table?

Bill

rleete · « **Reply #2 on:** August 12, 2012, 07:42:03 PM »

Re backlash: apparently, not well enough.

Yes, I have a rotary table. How would I hold a part like that?

b.lindsey · « **Reply #3 on:** August 12, 2012, 07:57:43 PM »

You could try super glueing it to a larger sacrificial piece that could be clamped to the rt. Center the rt, then without moving the table, nudge the mounted part till it is also cenrered with the spindle and then snug the hold down clamps.
Bill

steamer · « **Reply #4 on:** August 12, 2012, 08:17:49 PM »

Rleete
check my wallaby tbread...i us a glue chuck for a part like that

Dave

Jo · « **Reply #5 on:** August 12, 2012, 08:19:22 PM »

I agree with Bill, sounds to me like the backlash in your leadscrews is causing the problem. DRO's would solve this and do all the calculations for your cylinder head holes.

Another option is to use a chuck mounted on the rotary table.

Do you have bull wheel/indexing on your lathe? If so you could hold the cover in the chuck and think about mounting a drill on a vertical slide on the saddle and use that to drill the holes.

(I now use my DRO....

).

Jo

b.lindsey · « **Reply #6 on:** August 12, 2012, 08:51:45 PM »

Not that it helps at the moment, but an adapter for locating your lathe chuck in the center hole of the rt can be very handy. Its a feature i use often on my sherline rt, and can transfer parts from the lathe to the mill rt without ever having to remove them from the chuck. Obviously easier to do on smaller machines.

rleete · « **Reply #7 on:** August 12, 2012, 09:07:47 PM »

Bill, that's on the list. With the trouble I'm having doing these simple parts, it may have just moved to the top.

Nothing like ruining a few parts to really put the brakes on a build.

Ian S C · « **Reply #8 on:** August 16, 2012, 11:56:01 AM »

For 4, or 6 holes its easy to index it in the lathe, you don't need to drill it there if you are not set up for it. Put a center punch in the tool post, set it to the required radius, and as each index is done, bring up the punch and mark the work, remove from the lathe and drill. Ian S C

Mel Larsen · « **Reply #9 on:** August 16, 2012, 09:37:56 PM »

For about $800 you could solve your problem, buy a DRO for your milling machine. The hole bolt pattern thing was the first thing I praised after installing a DRO on my machine.
Mel

rleete · « **Reply #10 on:** August 17, 2012, 12:19:36 AM »

I was afraid that would be suggested. No way I'm putting $800 DROs on a $500 mill.

Mounting the part on a rotary table seems to be my best solution. I'll have to figure out a way to hold it down.

Mel Larsen · « **Reply #11 on:** August 17, 2012, 01:27:28 AM »

Heck, I put a $800 DRO and a $275 Table Drive on my $800 mill and think they are worth every penny, I can do thing now that I couldn't even dream of before. I was loosing interest before because of things I couldn't do.
Mel

steamer · « **Reply #12 on:** August 17, 2012, 01:31:03 AM »

Rleete,

one way to hold it down on a rotary table is to do a few holes and then shift the clamp, and do a few more. When I say shift the clamp, I mean put another one on first in another rotary position, and then take the first one off. Do a little more...ect.

Work your way around.

Dave

steamer · « **Reply #13 on:** August 17, 2012, 01:40:16 AM »

If you want Rleete....I can sketch something up .....just for food for thought ...let me know How many holes?

Dave

rleete · « **Reply #14 on:** August 17, 2012, 01:47:39 AM »

I think I have a solution for this one. I'm going to have to try and see if it works.

steamer · « **Reply #15 on:** August 17, 2012, 01:48:40 AM »

OK....take pictures!....

Dave

Pete49 · « **Reply #16 on:** August 17, 2012, 04:25:55 AM »

another ti if you like. Try Marvs site as I'm sure I saw a rogram for that purpose. But don't hold me to it I'm

and forgetful

Pete

Mainer · « **Reply #17 on:** August 19, 2012, 01:57:10 AM »

To ensure concentricity and solve the clamps-in-the-way problem, I have on occasion clamped a block of aluminum to the mill table, bored a snug sliding fit pocket for the cylinder head, not quite as deep as the cylinder head, and drilled/tapped a couple of holes next to the bored pocket such that the heads of binding--head (i.e. large diameter head) screws will overhang the pocket. Drop in the cylinder head, then thread in the screws and tighten down so their heads hold the part in place.

steamer · « **Reply #18 on:** August 19, 2012, 02:32:37 AM »

That's the fixture I was thinking of Mainer....but there are other ways.....

Dave

rleete · « **Reply #19 on:** August 19, 2012, 03:01:06 AM »

I made an arbor that holds the cylinder. No pics yet, I got sidetracked making the nudger that Bogs posted.

Still haven't drilled the holes, but I am doing machining for the first time in months.

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Author Topic: Circular hole pattern help (Read 8665 times)