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Precise concentric holes
- Thread starter AlexO
- Start date
- Replies 48
- Views 8,569
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
It's got be machined from one setting in the lathe, single point boring to keep the bores concentric etc etc etc
As for the 5 micrometer (micron) conentricity tolerance .........that depends on how good the lathe is, ........and AFAIK, there are very few machines in that class.
As for the 5 micrometer (micron) conentricity tolerance .........that depends on how good the lathe is, ........and AFAIK, there are very few machines in that class.
Monarchist
Diamond
- Joined
- Oct 2, 2012
- Location
- Sol, Terra
5 microns? BLIND hole from each opposite end, solid in between?
Buy the hole first from a specialist as a hard-vacuum.
Electroform the coupling metal around that precise vacuum - and slowly - so as not to stress the alignment OF the vacuum. Once done, admit ordinary atmosphere only through sub-micron filters, and at Standard Temperature and Pressure.
IOW.. who wrote that spec, and if he will not at least allow a through-hole, is his budget as big as his hunger, anyway?
The holes are one thing. The real cost will be in the workholding and f**k-with time.
Now.. if you only need ONE good one, and are willing to scrap 'several', to cherry-pick it?
It ain't actually that hard.
Do one hole. Set a precise shaft in it. Pick-up off that for the second hole, see what went sidegodlin, correct, compensate, try again, etc. I did say "f**k-with time"?
Helps, of course, if you've managed not only to have the hole DN concentric to the body, but can hold it just as accurately.
That is not assured for Joe Average, but is done every day, all day, by those who've made a business of it.
Sometimes pays to buy stock couplings and alter the rest of the design to match. Lot of that going around. Literally going around, and at serious RPM, as well.
Somebody is getting it right, already.
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
I'd be interested in how the 5 micron cylindricity spec for any one hole alone, gets done anyway....
Monarchist
Diamond
- Joined
- Oct 2, 2012
- Location
- Sol, Terra
Purchase order. Stock parts. Not my problem how.
How TF he expects to CLAMP the bugger to each of two separate shafts AND NOT depart that spec is far the greater problem that designer has to deal with. Set screws would make it a joke, for damned sure. Set a precision collet in each end? Heat-shrink? What?
Just have a look at the variety of clamping methods the major makers already offer. More than just a few methods on-offer out there, and that is a big part of the "why" of that.
The basic coupling tolerance is no harder than uber-precision roller bearings. Easier, actually. But we don't make those, either. We buy them from THEIR specialists.
Couplings, crude to precise, huge to micro, and all in-between, are also a mature industry.
FredC
Diamond
- Joined
- Oct 29, 2010
- Location
- Dewees Texas
You did not say what the OD is, if it is in the range that could be held with an accuracy 5c collet, I would bore and turn the finish pass consecutively so that both are concentric. Turn it around and fuss with a tenth (2 micron indicator) till you have it as good as you can, bore the second side.
You will not be able to do any better with the equipment mortals have, how is the end user going to prove it is not correct.
I have a fixture I routinely have set up. I can get it to indicate zero by fussing with it, I have a mark on the fixture that I line up with the 5C mark then rotate it back and forth from there till I get zero. the next time that is not good enough putting a little pressure on the fixture as I close the collet does the trick. Ten years after making it I can still get it to work be hook or crook.
You will not be able to do any better with the equipment mortals have, how is the end user going to prove it is not correct.
I have a fixture I routinely have set up. I can get it to indicate zero by fussing with it, I have a mark on the fixture that I line up with the 5C mark then rotate it back and forth from there till I get zero. the next time that is not good enough putting a little pressure on the fixture as I close the collet does the trick. Ten years after making it I can still get it to work be hook or crook.
Monarchist
Diamond
- Joined
- Oct 2, 2012
- Location
- Sol, Terra
Meahh... 10EE, 2J , Precise grinder touch up, many half-tenths dials in the drawers..
Make 20, ship the third best one, hold the first and second best, charge for the whole 20.. feign innocence and hand him a catalog when the fool tries to bitch after trying to clamp them?
I did say "f**k-with time" ? What's the point for a onesie, anyway?
Better-off to start with the catalog or a website link, ASK about clamping effects, and go do something less masturbatory while the designer furthers his OWN edumacation.
LKeithR
Stainless
- Joined
- Sep 1, 2011
- Location
- Langley, B.C.
Monarchist
Diamond
- Joined
- Oct 2, 2012
- Location
- Sol, Terra
Had to go back and read that one a second time...
Not original, sadly. Will Rogers era roots.
Early Texas wildcatter, 1930's, drilled a hole string of wannabee oil wells. Dry holes, every one, but damn if they weren't within 5 microns con-sin-trick-city thousand feet deep or no.
Was down to his last mess tin of frijoles when a flatland feather-merchant showed up with a deal to pull all them dry holes, chop-saw 'em into three foot lengths, and sell them by mail-order to farmers over in Arkansas as pre-fab fence-post holes to be set by maul. Saves a lot of diggn', that..
Got the first part done. Two man saw run one-ended, being no Harbour Freight just yet, and Tractor Supply selling nought but Alice Calm-hers tractors.
Had 'em stacked outdoors, unprotected. The holes. Not the tractors.
Y'know Texas weather?
Well a major duster came up. Wind-driven sand went and blasted crosswise holes all through the length of his stacked holes and rendered 'em unfit for sale. Can't have no loose dirt leakin' through the sides of a pre-fab hole 'fore you gits the post in.
Some folks would have quit, right there.
But its a Texian we are dealing with here, and "Quit" ain't a word common in their vocab-yew-lary.
Picked hisself up, went hard to work at his anvil, hammered them holey-holes into colanders, and made enough to put his grandkids through collitch to become "Design Engineers" on fine servo-mecha-nisms.
Never say "die" to a Texian!
Your clothing is like to change colour, and you'll be billed a stiff price for that service, teflon stain repellant an optional extra.
Last edited:
Milland
Diamond
- Joined
- Jul 6, 2006
- Location
- Hillsboro, New Hampshire
Could I poke my nose in here and confirm that you're looking for two coaxial bores of 8mm and 10mm diameter, not depths as I think some have interpreted your post? If so, then a single setup where you bore the 10mm, then the 8mm further in, will get your tolerance done as long as the lathe has good headstock bearings and decent ways near the spindle.
The point raised of what happens during the clamping itself is a good one, and should be addressed. Sometimes a circumferential clamp geometry can be incorporated into the coupling, if you do that with yours by roughing-in the bores to ~.1mm undersize, tighten the clamp screws a modest amount to preload the system, then finish bore for size and concentricity you can achieve a very good clamped axial accuracy.
Monarchist
Diamond
- Joined
- Oct 2, 2012
- Location
- Sol, Terra
+1 on the clamp pre-load. Similar to the common practice of closing an "emergency" collet on pins to go final.
Clamping at these tolerances - or far larger ones, even - is the overlooked Elephant in the room, actually.
So MIGHT ALSO be balance at speed, "servos" often having slew rates & c.
One of the few reasons for NOT using a stock coupling with inbuilt ability to deal with minor flex and misalignment.
So . not sure just what it is that drives an apparently simple dumb-old cylinder that becomes complex to make only when the tolerances enter.
Servos, resolvers, tachometers, tachogenerators, speedometers, timing and synchronizing mechanisms, and the like have been selecting successfully from such stock coupling options for longer than most here have been alive.
What is it - besides the Designer - that is "new" here?
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Rough bore, drill, whatever, both holes.
ID grind one hole.
Mount a oversized pin in a very good workhead and od grind it to within a few microns.
Mount the finish ground ID on the pin, ID grind the second hole.
Servos and solid couplings normally don't play well together though so the mounted to item needs to be floating or compliant in some form.
Works for say a mirror attached to a servo. Does not work for a ballscrew attached to a servo.
Bob
ID grind one hole.
Mount a oversized pin in a very good workhead and od grind it to within a few microns.
Mount the finish ground ID on the pin, ID grind the second hole.
Servos and solid couplings normally don't play well together though so the mounted to item needs to be floating or compliant in some form.
Works for say a mirror attached to a servo. Does not work for a ballscrew attached to a servo.
Bob
muckalee
Cast Iron
- Joined
- Jul 17, 2011
- Location
- Americus, Georgia
5 micrometers is 0.00019685 inch. What method and equipment is the customer using to measure the diameter and concentricity?
The tight tolerance, if correct, prohibits unclamping. So after having made both bores undersize, in one follow setup I’d ream the front and backwards turn the other bore to measure. 8 mm diameter is small but I think it’s feasible.
Reverse turning helps with straightness due to pulling.
Reverse turning helps with straightness due to pulling.
Sea Farmer
Diamond
- Joined
- Mar 25, 2006
- Location
- Cape Cod, Massachusetts
Had to go back and read that one a second time...
Oh we all have to do that with all of his posts.
Be kind to the elderly, some day it will be you and me writing this stuff. I'm getting closer
The holes are trough and material is not critical. And there is very little torque transmitted. I can get the 10mm one - the 8mm is killing me.
Actually, given the general size of the coupling 5 microns is not that tight.I was thinking of splitting the coupling in two "flanges", lap each in a fixture and then assemble with screws or glue. But it's tedious and I need to make around 20 of those.
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
"Actually, given the general size of the coupling 5 microns is not that tight."
What temperature do you want them to be within 5 microns?
Reminde me, was that 5 microns TIR or +/- 5 microns?
What temperature do you want them to be within 5 microns?
Reminde me, was that 5 microns TIR or +/- 5 microns?
It does not matter - the major problem is to keep them concentric within 5 microns.
I don't have a jig borer, unfortunately.
johnoder
Diamond
- Joined
- Jul 16, 2004
- Location
- Houston, TX USA
Maybe not as soon as you think. This 77 year old still generates plain speak - and aspires to do the same as long as that portion of the assembly functions
Oh we all have to do that with all of his posts.
Be kind to the elderly, some day it will be you and me writing this stuff. I'm getting closer
