Errors multiplying in a Rivet Spacer

[teenylittlemetalguy]

So I made this rivet spacer. it is not perfect, but is accurate enough for my uses.
(not using it in machining)
As you can see from the photo I had to drop a few rivets. Obviously in a situation like this the small errors multiplied to give me my headache. My question is about layout.
I laid out one leg very accurately and used it as a guide. should I have laid out each hole separate?
My guess is the errors came in towards the end of the process as the guide got less accurate each time I used it.
Could I have just made two guides and switched towards the end, or buckle down and let my brain go numb while I layout nearly 100 holes?

[Cross Pein]

Pardon my ignorance, but what am I looking at here. 

Never mind, I googled it.

 

If it were me,  I would make a jig for my drill press.  That way I would only need to lay out the first hole on each bar.

Something where the last hole drilled went over a pin to get a consistent distance and some sort of fence for the side to side.

 

You could also assemble it with the minimum necessary and drill the rest two pieces at a time.

 

Good luck,

Bill

[781]

When laying out you need to start at the end and keep measuring from the same end not hole to hole.

[K. Bryan Morgan]

That is a nifty gadget.  I like it.  I think your issue is tolerances.  You want the holes just a tiny bit over sized.  If there isn't any tolerance, say like .003-.005 over sized, it will never work correctly.  It will be to tight and not go together.  I had to go though all of that in school a lifetime ago.  Just my thoughts, but if you waller out the holes just a little bit, I bet you dinner it will go together just fine.

[Larry H]

lay out your jig, if it's 3", 4",  or  2 & 3/32....every hole will be the same distance apart

[Glenn]

I found a 10 hole rivet spacer for $25 and a 20 hole rivet spacer for $40 on line. You have to decide if the project justifies the expense for such a tool.

 

My suggestion would be jig up and have a control pin (or two) to check each new hole. If you drill multiple pieces at the same time you have a better chance of getting the same hole pattern (either good holes or a bad hole). Keep a sharp drill bit and lots of cutting fluid so you get clean holes.

[HWooldridge]

When you say one leg was laid "very accurately", what does that mean? Did you use layout blue and a scriber? A silver pencil is several thousandths wide so it's easy to compound an error - chalk is even worse. A better way would be to drill the holes on a vertical mill with a DRO while spotting each hole with a center drill. I'm with Glenn on this one - easier to buy one made specifically for the task.

[teenylittlemetalguy]

I agree it would be easier to buy one, but the point for me is the capability to make one rather than the owning of it.
I did actually make a jig, laid it out with bluing and was in the .001-.005 range before I center drilled. The guide came out nicely. I clamped the pieces one at a time in the jig to avoid the errors that happen when drilling through thicker stock.
To me the variables I didn't control well were the actual stock probably had some small bends from the cold roller and my jig did not force to the center of the bar (left that to my eye, which I now know is a mistake.)

[Frosty]

Tristan: Am I mistaken in thinking you Drilled using the template as a guide? that is NOT an accurate method as the bit WILL walk around a couple thou. at best. For this (machine shop) work there is NO SUCH THING as a "jig." Even duplicators or pantographs are NOT jigs, they're accurate, repeating measuring devices.

 

For accuracy: #1 Always measure from the same initiation point and add increments to the measurement. Adding by increment from the proceeding point multiplies inaccuracies. #2 Use thicker stock for the template, say 1/4" minimum, 3/8" better. #3 temperature counts so measure at a consistent temperature for both template and stock. #4 Use a transfer punch, NEVER EVER drill through the template, even welded it will walk. (wobble).

 

The technique you use drilling the holes counts. Slow RPM will drill closer to the stated size of the bit than faster RPM. The faster it turns the more it WILL wobble (wallow). Down pressure will effect hole size and circularity as well, the lighter the down pressure you use the more oversize the hole will be. What happens is friction induced heat will be carried into the base stock and bit, instead of being carried away with the cuttings. Two things not good happen when the base stock and bit absorb heat, most significantly the enlarged bit drills a larger hole. The trick is sharpen the bit precisely and learn how much you can hog the feed without over heating it. This is done mostly by sound and drill reaction. Use low RPM and hog the feed at optimum cutting conditions will yield the most accurate and more importantly to you, consistent hole sizes and positioning. Did I mention getting the stock hot will spread the holes farther? ( I KNEW I included heating the stock for some reason!) All in all we can be talking only a couple ten thou per hole but when we're talking about 20-40 holes compound error quickly reaches over all failure conditions.

 

For the initial layout you can get reasonably close, say a couple thou, using Diechem Blue, a close (as in machine shop accurate) scribe and calipers. Dad would kill me for suggesting this but if you have a very light touch you can use the ID points on a pair of calipers to scratch (LIGHTLY!!) through the Diechem but you'll need to polish the template stock first so it'll show. Of course it IS a template and can be aluminum which will make drilling easier to be accurate but you'll need to "normalize" the temp in water or oil before every hole.

 

Do you have a Pilot bit? Can't beat a good pilot bit for starting holes accurately. When you say "center drilled". Are you saying you pilot drilled each hole? I can not see where a center hole is necessary. A pilot bit is a drill bit commonly used on a lathe to drill a shallow center hole to initiate a bore hole so the drill bit or the stock won't wobble (walk) starting the hole. In flat stock on a drill press a center punch CAN fill this purpose but for accurate use a pilot bit.

 

Tell you what, I can show you far faster than I can describe the process. When can you make it out again? My drill press is easier to use simply because it's at better working/eye height and I have pilot bits, calipers, machinist's scribe, etc. Better, there's NO way I can describe what optimum drill hogging sounds and feels, you just gotta see, hear and feel it, then take a slash at it yourself while I kibitz.

 

Oh yeah, I'll show you how to sharpen drill bits on a wheel with a gage, not that sharpenting "machines" don't work well but if you know how to do it on a wheel by eye and hand you won't be up a creek without a paddle if the sharpener isn't handy.

 

Frosty The Lucky.

[teenylittlemetalguy]

Frosty, thanks, that is what I needed. I did drill through my template.8-( that is likely where most of the errors came from. sounds like mostly every thing else I did right. I have a countersink/center drill. beefy 1/2 bit with about a 3/16" dill point. it gets holes started for me pretty good. the drill bit I followed up with was fairly sharp, but I bet it could use a little touch up first.
I would like to take you up on that offer of looking over your shoulder at the process.
We are expecting our baby any day now so I need to stay close to home. Hopefully sometime in February I could come out for a couple hours on an evening?
Thanks again, I really appreciate it.

[fciron]

If I need to use a template multiple times and want to preserve accuracy, I will transfer punch through it rather than drill. The transfer punches don't wallow out the holes the way that a drill bit will.