Precision hole drilling

Making of encoder mounting plates requires several accurately drilled holes. I already made one plate and it seems to work, but I had some
problems/issues with placing holes precisely.
The material is brass (it was a great idea to use brass).
I calulated all hole positions using a spreadsheet. See "Encoder Mounts" sheet here:
http://spreadsheets.google.com/pub?key qcJgZET_M0ddGpQSHlWajM3UHBCRXRTRlBGbnp2Mnc&hl=en&output=html
To fit it over a 17mm motor shaft, I had to drill a 43/64 hole. (17.065mm).
I do not know of any way how I could drill that hole precisely, with a huge (comparatively) MT3 drill bit, as any drill bit would wander away at least somewhat, I think.
So what I did was, I drilled the 17mm hole aproximately where it should be. Then, with DRO, I located the center of the hole and then moved to what should be a point (0,0), based on the calculated position of the center of the hole. (kind of a backwards thinking process).
For smaller holes, all I did was start them with a center drill and then drill with a drill bit.
It actually seems to have worked, as the encoder works just fine.
When making that mounting plate, I realized that there is a lot to precision drilling, and want to ask now if anyone knows tricks for drilling precise holes. I have two more plates to make.
The required precision for locating encoder base is 0.01". (which is not that bad).
On a related note: to bolt the base to the motor, I had to drill four holes for the mounting bolts. How can I precisely measure the distance between holes. I tried using a caliper and it worked, obviously, but I can not be totally sure how accurate I was. I would measure the distance between two points in holes closest to one another, then farthest, and average the two. But it felt that there was a lot of wiggle room in those measurements. SEM has a manual for the motors in question and it specifies the distance, but based on what I drilled, the distance is slightly wrong. (the motors were made 20 years ago)., I was lucky that I drilled the holes slightly oversize. For the next pair of plates, I would really like to drill to-size holes in the right place.
i
i
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This is where autocad is a great tool. Draw it and print full scale. check paper against part.
From there, you have all your holes centers and diameters. use a center drill or spot drill (my favorite) then drill each point. A CNC machine is best <Grin>, but a DRO works too. Do your milling at the same time.
Karl
P.S. Find me a deal on a Leblond servo shift and I'll make the parts for you.
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Karl,
I disagree. If he has the money for the CNC, then he should buy a multi-spindle drilling head from those AutoDrill guys and do it in one stroke. That way, the head manufacturer is 100% liable if the pattern comes out wrong. A drill bushing plate could help with the oversized issue too... But to create that plate is more work than the single part I presume he needed.
<grinning wildly at the misapplication of technology I have just suggested>
--


Regards,
Joe Agro, Jr.
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Karl Townsend wrote:

laser printers have gotten a LOT better since the early ones, but they are still very inaccurate. If you can get .050" accuracy over the whole sheet of paper, I'd be amazed. I'd NEVER try to do precision work this way. print a document twice, once with mirror printing on, and hold the two up to a light to see how well they align.
Jon
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You misunderstand me. this is not for tolerance, its for finding your gross measuring errors. I agree, the printer isn't exact, but it will quickly spot a measurement error.
Karl
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I did some sanity checks in the spreadsheet.
i
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Jon Elson wrote:

I printed some CD labels a while back that the foreground image was not printing. But the circle of the CD outline did - about .010 wide.
Four passes on a cheap Lexmark X2550 - Four paper reloads on the same page.
Absolutely beautiful registration.
Perfectly round with no widening of the line anywhere.
But I'm not mirroring anything.
Why would I want to???
--

Richard Lamb



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    In particular -- the linear dimensions across the short dimension of the paper tend to be more non-linear because they are drawn with a rotating mirror and the laser -- trying to convert angular motion to linear motion -- (with optics which attempt to correct the linearity -- but are not perfect). The other axis is defined by the paper being advanced by stepping switches, and might actually be more accurate if the advance rollers do not slip. (Some plotters actually have grit on the advance rollers which form a track in the back of the paper, so it moves the same distance for all the passes back and forth to draw the whole image. Overall, a good plotter is more accurate (at least to start with) though the paper can shrink or swell with humidity changes, so use it as soon after plotting as possible.
    Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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DoN. Nichols wrote:

Laser printers can produce accurate and very useful images. Years ago I built a device for aligning optical read heads. It used a laser- printed pattern revolving on a drum. We *knew* the inherit limitations of paper and intended to get the final pattern photoplotted on Mylar, but the paper pattern, printed on high quality card stock was accurate enough (a couple thousands over 1" and a few thousands over 8") and had much better contrast so we ended up using it.
That was with an old Laserjet II. All bets are off with the current batch of cheap printers.

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Actually there are laws that prevent much better if that good.
I remember when the first non-IBM color came out. It was experimental and expensive. The Treasury / FBI visited, tested it and made them tune it off just a tad to pass their test. It was technically perfect from a very high tech group of designers. It was to good.
It is the rules - must be just a little wrong.
One of the reasons we catch so many copy machine money makers.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net "Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
On 7/13/2010 2:20 PM, Jon Elson wrote:

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On Tue, 13 Jul 2010 22:46:35 -0500, Martin H. Eastburn wrote:

I don't believe it. Got any references?

Perhaps you are thinking of the color laser yellow dots forensic watermarking technique used in many color lasers. Apparently there are no US laws as such about this, but it is true that printer makers usually make their color lasers print a scattering of otherwise superfluous yellow dots that specifically identify which printer printed a page. In the main this doesn't compromise dimensional accuracy or other colors.
<http://www.eff.org/issues/printers explains the problem and has links to a dozen other articles, with titles such as "Laser Printers Reveal Your Identity Through Dots", "Instructables.com tutorial demonstrating how to view printer dots", "EU: Printer Tracking Dots May Violate Human Rights", and "List of Printers Which Do or Do Not Display Tracking Dots".
--
jiw

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Ignoramus3537 wrote:

http://spreadsheets.google.com/pub?key qcJgZET_M0ddGpQSHlWajM3UHBCRXRTRlBGbnp2Mnc&hl=en&output=html
For all of the holes, you should be spotting them with the short flex-free center drill to get started on center without wander. You also need to plunge the center drill down solidly to start which also helps ensure it doesn't wander. After center drilling switch to regular drill bits, but work your way up to the final hole size in a few steps if it's a larger hole. If you really want a good hole, you drill up to a size a few thou short of the final size and then ream to final size.
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DRO ??
Bob Swinney
Making of encoder mounting plates requires several accurately drilled holes. I already made one plate and it seems to work, but I had some problems/issues with placing holes precisely.
The material is brass (it was a great idea to use brass).
I calulated all hole positions using a spreadsheet. See "Encoder Mounts" sheet here:
http://spreadsheets.google.com/pub?key qcJgZET_M0ddGpQSHlWajM3UHBCRXRTRlBGbnp2Mnc&hl=en&output=html
To fit it over a 17mm motor shaft, I had to drill a 43/64 hole. (17.065mm).
I do not know of any way how I could drill that hole precisely, with a huge (comparatively) MT3 drill bit, as any drill bit would wander away at least somewhat, I think.
So what I did was, I drilled the 17mm hole aproximately where it should be. Then, with DRO, I located the center of the hole and then moved to what should be a point (0,0), based on the calculated position of the center of the hole. (kind of a backwards thinking process).
For smaller holes, all I did was start them with a center drill and then drill with a drill bit.
It actually seems to have worked, as the encoder works just fine.
When making that mounting plate, I realized that there is a lot to precision drilling, and want to ask now if anyone knows tricks for drilling precise holes. I have two more plates to make.
The required precision for locating encoder base is 0.01". (which is not that bad).
On a related note: to bolt the base to the motor, I had to drill four holes for the mounting bolts. How can I precisely measure the distance between holes. I tried using a caliper and it worked, obviously, but I can not be totally sure how accurate I was. I would measure the distance between two points in holes closest to one another, then farthest, and average the two. But it felt that there was a lot of wiggle room in those measurements. SEM has a manual for the motors in question and it specifies the distance, but based on what I drilled, the distance is slightly wrong. (the motors were made 20 years ago)., I was lucky that I drilled the holes slightly oversize. For the next pair of plates, I would really like to drill to-size holes in the right place.
i
i
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Drill relocation option.
Special tool on his mill.
(Digital Read-Out) <G>
LLoyd
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On 2010-07-13, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

I have a DRO. The issue is, if I move to point (1.2345, 6.5432), and plung the drill down, will the hole really be in thast point or somewhere close due to drill wandering.
i
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Ignoramus3537 wrote:

The hole will be at that point it you use a suitable center or spotting drill (short and stiff), and plunge fast enough that it bites properly before having and opportunity to wander. You should also be using a fairly high spindle speed for the small drills.
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Please just drill them close to size and then bore them. You must have a boring head.
JC
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Iggy, you understand he doesn't mean plunge the 43/64" drill. He was talking about a short, rigid spotting drill.
Unless you've got lost motion in your system, it should be close enough; WAY tighter than your spec on those mounts.
It cannot hurt, after dialing to your location, to lock both ways and just barely gently snug up the quill lock. Re-check that the way locks didn't move the table, and that the quill lock didn't push the quill out of line. Unless your machine is quite worn, it shouldn't.
I personally wouldn't drill such a hole in that thin stock. I'd drill/ream or bore it to finished size. A trick I'm partial to is to mount a boring head in the tailstock, and use the head's vernier to adjust the hole size. There's no difference in the finished job between doing that or just using a boring tool on the post, but it is faster and more convenient for me to do it that way if I don't already have a boring tool holder in the toolpost. (I have a homebrew indexable post that is anything BUT "quick-change").
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

It might have been appropriate to say, "when I'm drilling in the lathe..."
Duh!
LLoyd
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Ignoramus3537 wrote:

OK. With the DRO, it is doable to get well-centered holes. For the central hole and any locating bosses, use a boring head and boring tools. You can set the exact diameter needed, the hole will be aligned very accurately. For the bolt holes that will likely have a little slop anyway, use a center drill first, then change to the jobber's length drill and drill to size. it will be quite well centered, probably within .003" or better of the table's position. The bored hole will be within .001".
Jon
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