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Thread: 0.3 Module Gear Cutting Query
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18th August 2015, 04:39 PM #1.
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0.3 Module Gear Cutting Query
I need to make a replacement fine focus gear for an early '70s Nikon S microscope. The original gear is nylon with a brass hub and it is commonplace for the nylon to split which is what has happened to mine. Spares are no longer available.
The gear has 107 teeth, a pitch diameter of 32.10mm and a 20 degree pressure angle. I have not removed the gear from the scope but photos of others online would suggest a thickness of about 5mm.
I have looked online for cutters and while there are some in the Ukraine, something closer to home or possibly even home made has more appeal.
Would a single point fly cutter be up to the task? Whether I'm up to the task of grinding the cutter is something else.
BT
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18th August 2015 04:39 PM # ADSGoogle Adsense Advertisement
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18th August 2015, 04:47 PM #2
You could certainly use a fly cutter to do it, but as you mentioned you would have a hell of a time grinding the profile.
Maybe you could use a magnifying glass when grinding the profile?
Can you buy a similar gear? Wouldn't matter if it was thicker or had a different hub.Cheers.
Vernon.
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18th August 2015, 05:04 PM #3GOLD MEMBER
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That's what optical comparators are for Bob!
If you wait long enough I'll grind you one on the Wickman..... I doubt you'll want to wait THAT long lol
You dont say what you'll be making the replacement out of, though for a one off, I doubt it would matter.
Stuart
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18th August 2015, 05:25 PM #4.
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Vernon,
Seeing what I'm grinding wouldn't really be an issue, it would be an ideal opportunity to use one of my stereo scopes. As far as buying an over the counter gear that matches the original goes, any suggestions? I looked at HPC Gears and they offer a 108 tooth gear. Close.
And Stu, yes the comparator might prove real handy. The gear would be brass.
BT
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18th August 2015, 07:05 PM #5
Yeah I did have a look for a stock gear, but could only find this anti-backlash gear - http://www.reliance.co.uk/shop/produ...ath=32_355_362
EDIT - here is one from the same mob - http://www.reliance.co.uk/shop/products.php?17530Cheers.
Vernon.
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18th August 2015, 07:14 PM #6Philomath in training
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I'm sorry to say that I can't help you there Bob as my smallest cutter is M0.5.
This article explains how to make a form cutter -
http://www.metalwebnews.com/howto/gear/gear1.html
Which I think is probably less stressful than trying to grind a fly cutter symmetrically.
However, your depth of cut is only 0.65mm - not very big!
Your last problem is the number of divisions. 107 is not in the common ratios for dividing heads or rotary tables. Do you have the set up for differential indexing?
Michael
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18th August 2015, 07:19 PM #7Cba
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Bob, here is a set of 8 M0.3 involute Module gear cutters from Belarus - US$80 is quite a bargain, less than $9 each and postage is free:
http://www.ebay.com.au/itm/Involute-...item3f45ebc89d
And no time spent on painfully grinding a form tool (M0.3 is pretty small, you may even need to buy a tiny ponted grinding wheel to make it). And if the profile you grind is not quite right you are left living with a sloppy or sticky gear in your microscope.
I have previosly bought several such sets, from another seller in Ukraine. These are new old stock from the Soviet time. They usually have some stains and some may even have light surface rust - no surprise after 20+ Years storage. Being form cutters, these are easy to re-sharpen if necessary. It may not be the best quality HSS, but hey at that price who cares, and if its only hobby use they do not need to last to cut 5000 tooth... One set that I only needed once (it was an odd Module dimension, M0.9 if I remember well) I even sold it again on eBay for more than what I originally paid for. Standard postage may turn out to be faster than ordering such a set from Australia for 4 times the money. And if you bought such a set in Australia and decided to sell it after you made your gear, you would only get 20 or 30% of your outlay back.
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18th August 2015, 10:58 PM #8.
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Well, it's looking pretty much like I'm stumped before I even start. I have no way of creating 107 divisions. 106 and 108 , sure.
Thank you all for your suggestions.
Bob.
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18th August 2015, 11:31 PM #9Novice
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Bob, what dividing head do you have? Do you have a rotary table? If so you could make a special 107 plate for your dividing head on the rotary table without the need for differential indexing. Just a thought! Then again, if you only want one off then just use the calculated angular spacing on the rotary table.
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18th August 2015, 11:33 PM #10GOLD MEMBER
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I'm not so sure I'd be worry about plates.
If you dividing head is 90 turns and my maths is right. If you just dial in deg,min.sec*, your greatest error would be something like 1 min 20 second**. Is that really going to worry anything?
If so then make a plate as above and use that to divide your gear. The error will be 1/90th of the above.
If you're still not happy, use that plate to make another plate
Failing that you can use x/y coordinates and mill yourself one
Regards being "left living with a sloppy or sticky gear in your microscope"
I would have thought the gear train was spring loaded so a "little sloopy" wouldn't hurt anything as the backlash will be removed????
Stuart
*I've done it for 41 divs and had to go around 4 time I think, but I only went to the nearest minute.
** still checking that.. it might be even less. Much like "how close does thread pitch need to be... how close do teeth have to be to perfect?
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18th August 2015, 11:47 PM #11GOLD MEMBER
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Changed my mind, the error would be (in theory) a max of 5 seconds....I wonder if the worn is anything like that good anyway?
Stuart
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18th August 2015, 11:51 PM #12SENIOR MEMBER
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CAD + 3d print ?
Bob,
You could make a cad file of the gear wheel and send it to a 3d printing place and they could make one for you. Might be expensive, but you've probably got access to the 3d printing folk on this forum who might help. Exchange favours with somebody.
There would be a few packages around nowadays that you could do that with. You just key in all the data and it draws the part ie Z teeth Y pressure angle X module etc examples would be inkscape, or gearotic, or the woodgears prgram.
However it could be offensive to the mindset of the bloke in the shed who wants to do all the interesting stuff himself, but I wouldn't tell anyone if you did it.
Bill
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19th August 2015, 12:34 AM #13
Hi Stuart, BT,
Making the dividing plate wouldn't be too hard, with the PCD program in the DRO it would be easy enough? ( famous last words)
I looked through the box of cutters I picked up in an auction lot, smallest was 0.5, I thought there were smaller ones in there, but no joy ( sorry).
Ray
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19th August 2015, 12:43 AM #14.
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One of these Rusty - The direct indexing plate and arm can be removed and replaced with a worm and division plates.
045 (Large).JPG
A plate could be knocked up I guess using the rotary table.
Stu, Schaublin use a 60:1 ratio.
Bill, we have a 3D printer at work. I asked whether it would be capable of recreating the gear and was told that it wouldn't. It's used for small architectural model making. From what I have seen of its creations, they lack fine detail. The bloke most versed in the use of the printer did tell me how I could go about having the gear printed by an outside source. My problem was/is the production of the drawing. The only bloke in the office who would have an inkling of what a pressure angle is can't draw in CAD. I'll ask about the programs you mention tomorrow.
As far as the DIY thing goes, I'd buy a gear it it was available rather than fool around making one. The stainless gear that Vernon linked to has an appeal but I don't know how well and for how long it would work with the brass gear that it would engage given Nikon's choice of nylon for the 107 tooth gear.
Bob.
PS thanks for looking Ray.Last edited by Anorak Bob; 19th August 2015 at 01:00 AM. Reason: PS added
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19th August 2015, 08:02 AM #15Philomath in training
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The design of these gears is that they are pressed onto a bearing outer - so the gear itself is under (circumferential) tension when installed. Chances are that is why the original one broke. It depends on the process but some of these printed parts are nowhere near as strong as the solid material that you would otherwise use. The teeth on this gear are only 0.65mm high too, so would need really good definition. While I'm not saying that a 3D printer could not do it I think you would be running up against practical difficulties getting the detail fine enough in a part that has sufficient strength.
Michael
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