Author Topic: Accurate Drilling - centering microscope, USB cam, optical punch?  (Read 28322 times)

Offline Lew_Merrick_PE

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #25 on: June 27, 2011, 11:02:49 AM »
Lew surely the whole problem that Chris has using a depthing gauge is that he does not know how far to wind in the dial or read off the DRO so there is little point in establishing a zero.

At best the hole will be located a set distance from one edge and at its intersection with an arc, at worse it will be at the intersection of two arcs so you can't use co-ordinates to position the hole.

As for round holes when clock making isn't that what they make broaches for, bit like a reamer but produces a round hole in sheet material.

Jason,

The positions you cite (distance from one edge & intersection with an arc or an intersection of two arcs) is geometry that can be calculated in terms of X and Y coordinate values.  Yes, there are many times when transferring geometry is simpler, but it is rarely more accurate -- and accuracy is stated as a concern.  I admit that I have never made a clock.  Travel and test dial indicators, yes.  Clocks, no.  Finding the coordinates of an intersection between an arc and either another arc or a line is the base application for the solution to a Quadratic equation that we all had to memorize at some point in school.  We do it quickly and painlessly today using CAD software.  ???

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Edit, is this the type of drill bit?
[/quote]

Those are similar, but they are ground for drilling (burning might be a better descriptions) holes in hardened steel.  If you found one in the proper size, you could regrind the point.  The sheetmetal drill bits of my youth were fairly common -- and I spent more time than rational trying to find a source for them a few years back.  I ended up making a small set of them for a client and they were thrilled.

 .

   Lew

Offline kwackers

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #26 on: June 27, 2011, 04:03:14 PM »
I can't believe people are seriously considering replacing a perfectly simple tool that can obtain the ideal mesh between two gears and transfer those points to a plate with as close to perfect accuracy as it's possible to get with a system that still requires the tool, suitably modified to enable the distance between the two points to be accurately determined and then the numbers crunched in a CAD package before finally being entered into the DRO.

Why make things so complex?

Offline Miner

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #27 on: June 27, 2011, 05:02:39 PM »
I've certainly learned far more about just how clockmakers lay out the holes than I knew before. Since I obviously still know very little about this my comments could be a total waste of space on this thread.

It seems to me that the inaccuracys are mostly due to the prick or center punching as your depending on feel and normal eyesight to get those punch marks aligned at the true center of your layout lines. If the punch marks are even slightly out then the drill will drop into that punch mark and you then have a misaligned hole. I'd delete the punch marking completely since there's no real way to get consistant and accurate results.

As people have mentioned, Those spindle mounted web cams would be your best bet IF you can get a consistant alignment with the cameras cross hairs and the spindle C/L. IMO a dedicated web cam mount like a end mill holder that uses set screws to retain the end mill and fits the mills spindle would be a priority. If your spindle allows rotation of that web cam/end mill holder like a mill with a M/T internal taper would, Then marking both the spindle o.d. and the holder so they always go back into the same position would be a nessisity. Those high end German made 3-D Tasters use the same idea to get accurate and consistant results. The old school clock makers didn't use anything like a web cam and everything was done by hand and eye. But there's no doubt if they had what we do today they would have dumped the hand methods in a second. Other than your absolute need and the requirements to use a depthing tool, For myself I've given up on center punching work that requires accuracy and use the coordinate system. You then start from a referance point. The old school (non cnc) super accurate Moore jig boring and grinding machines used that system, So if it was good enough for them.............

Pete    

Offline John Hill

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #28 on: June 27, 2011, 05:20:19 PM »

I don't follow, where did the paper drawing come from? Did you draw it yourself? If so how's that easier than simply marking out using a depthing gauge?

I think people are getting carried away here, marking out clock wheels using a depthing gauge and then drilling the points isn't a big issue. It doesn't need to be super accurate on a per hole basis but it does need to allow for accumulated error.
The system of using a depthing gauge and drawing arcs fits those parameters perfectly. As soon as you start measuring and calculating you accumulate errors and risk the whole thing going pear shaped.


You need some idea of the layout of the gear train unless you have designed the clock entirely in your head.

Here is my suggested process in some detail.

1. sketch layout of gear train.
2. use depthing gauge to determine distances between drill points and mark these on your sketch.
3. drill first hole.
4. refer to sketch for distance and direction to next hole.
5. use DRO to position for next hole.
6. drill
7. rinse, lather and repeat.

Note that each position is determined relative to the one before therefore errors do not accumulate.

From the den of The Artful Bodger

Offline PekkaNF

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #29 on: June 28, 2011, 01:37:17 AM »
Really great thread. Like this formum. People from different backgrounds and disiplines tell how AND why they use the method and how it works from them. I never build a clock and have found it hard to understand WHY they do gear train the way they do, but I think it's dawning to me now. In principle, it's not that fundamentaly different from how gear train is build on banjo before thread cutting...

IMHO if centre punching is used, it needs practice. Least for me: I need small and sharp 60 decree punch to find the centre of two scribed scores, held perfectly straight up, then gentle tap and checked with magnifier. Haven't noticed difference between 60/90 decree punch marks when I have used NC-spotting drills, twis drills seems to need 90 decree punch, although I have found out that too big "crater" for the drill size is not a way to go.

Does anybody use a conical wiggler or sticky needle to center spindle to centre punch?

How small holes we are talkking on this thread? I have't found smaller than 3 mm spot drills, but years ago we used PC-board drills to make 0.5 - 1.2 mm holes. They were britle and run very hight rpm, but worked then fine on good drill press.

Pekka

Offline picclock

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #30 on: June 28, 2011, 02:48:09 AM »
The problem as I understand it is to accurately transfer a running gearfit dimension to the plate to be drilled.

As a possible thought, has anyone considered making the chuck on the mill part of the depther. So to get a correct gearfit, utilise a spindle with the gear fitted into the chuck and the meshing gear and spindle fitted to the plate. An additional block may need to be made to ensure that the plate gear spindle is truly vertical, just a block with a long hole on the top to align the spindle, the bottom part of which can be milled away to clear the gear. This method would allow adjustment of the fit to the correct distance, then the spindle in the chuck could be replaced with a centre for making the drill start.

This eliminates the depther and should give far higher accuracy without any need for centre punching or transfer of dimension.

Hope it makes sense.

Best Regards

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline kwackers

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #31 on: June 28, 2011, 04:32:43 AM »
You need some idea of the layout of the gear train unless you have designed the clock entirely in your head.

Here is my suggested process in some detail.

1. sketch layout of gear train.
2. use depthing gauge to determine distances between drill points and mark these on your sketch.
3. drill first hole.
4. refer to sketch for distance and direction to next hole.
5. use DRO to position for next hole.
6. drill
7. rinse, lather and repeat.

Note that each position is determined relative to the one before therefore errors do not accumulate.

My problem with that is measuring the distance between the points on the depthing tool with any accuracy.
Where you have a train of gears the inaccuracies add up.

Although tbh I think everyone is thinking like engineers and as I said earlier, engineers build poor clocks for the simple reason they make everything an engineering fit...
Clocks aren't made that accurately.

The most important bit is finding the correct mesh between two gears and the distance between them. Once you have that you can happily drill the hole by eye on a pedestal drill - don't even need a mill...
Whilst 10 thou might be a bit poor getting it within one or two isn't an issue - there should be around a thou play in the axle anyway! The holes for the axles are usually tapered too so has to prevent any chance of racking jamming the gear.

The problem Chris (OP) has is he's thinking it all needs to be super accurate, it doesn't. It needs to be free.

Offline John Hill

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #32 on: June 28, 2011, 04:45:16 AM »
Kwackers,  I see little point in explaining further so I and done with this.
From the den of The Artful Bodger

Offline raynerd

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #33 on: June 28, 2011, 05:05:47 AM »
The most important bit is finding the correct mesh between two gears and the distance between them. Once you have that you can happily drill the hole by eye on a pedestal drill - don't even need a mill...
Whilst 10 thou might be a bit poor getting it within one or two isn't an issue - there should be around a thou play in the axle anyway! The holes for the axles are usually tapered too so has to prevent any chance of racking jamming the gear.

The problem Chris (OP) has is he's thinking it all needs to be super accurate, it doesn't. It needs to be free.

Qwackers, I know in Colin Thrones Book - "Clock Building for the Model Engineer" he just explains that the marked out points are then drilled - he doesn`t say how and I presume it is just done by eye. What would be your method, centre pop and then drill ?  The hole I`m drilling is 0.8mm so literally, how would you go about from a marked out point to drilling the small hole?


I`ve been watching every single post made in this thread with interest and I didn`t want to throw in any stupid comments so I have stayed out. My issue does lie as many have said with having a hole with no co-ordinates and therefore just wanting to drill from the marked point hence the suggestion that an optical scope or punch may be needed.

You have all made many very very good suggestions but I would like to consider my options now as if a DRO was not available and just spot drilling to a cross marked position.

 :mmr:   I am kind of pleased that my thread has sparked all this discussion and that my issue is clearly one that can be done in many way as I presumed! I just find when I currently mark out my position and then drill a hole, the hole is not perfectly central to the "cross hairs" mark! A few have suggested a pointed in the chuck/collet - this could possible work well!
Chris

Offline Jasonb

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #34 on: June 28, 2011, 12:13:31 PM »
As I said use a sharp DOT punch not a centre punch. Lean it slightly so you can see the end as you place it on the intersection of your two marked lines, you should be able to feel it sit into the scribed line. Bring it vertical and give a light tap, inspect this punch mark with a magnifying glass, if it is off the punch can be tilted and tapped at an angle to pull the punch mark to where you need it. Once happy with the dot punch mark follow up with a sharp centre punch.

You can then locate the centre punch mark in your drill or mill with a centre finder, the pin type will do and drill your hole.

Jason

Offline kwackers

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Re: Accurate Drilling - centering microscope, USB cam, optical punch?
« Reply #35 on: June 28, 2011, 01:03:09 PM »
For most of my drilling let me just say that I co-ordinate drill using my DRO.

In cases like clock frames though I simply blue and mark using proprietary tools - i.e. a depthing gauge.

The depthing gauge works best if a small centre pop'd mark exists in order to more easily register the point of it's shaft, then I draw the arc, mesh up the next gears and continue.
The centre pop is done as Jason says above. You can feel the intersection of the arcs with it's point, then keep it dead vertical and a light tap - you hardly need to be able to see it.
Inspect it and if necessary you can adjust it slightly but with a bit of practice you won't need to.

Then I put the frame on my mill (I use the mill because it's easy to move the frame accurately).

In your case with a 0.8mm drill I'd be happy to line that up by eye - although I find it much better to do it whilst it's spinning, otherwise the facets of the cutting edges can throw you.

But for most stuff I use a wiggler set - in particular the pointy tool (follow link for an example)
Wiggler Set on Amazone
You put the wiggler in the chuck, spin up the machine and just lightly touch the pointy bit with a pencil, this will make it run true and the very sharp point means that with my now obligatory magnifying goggles I can (according to my DRO) see an error in the order of a couple of tenths - providing I wasn't too heavy handed with the punch...