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Thread: 0.3 Module Gear Cutting Query
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21st August 2015, 03:38 PM #46SENIOR MEMBER
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Sweet as Bro-Bob! That's exactly the sort of thing I had in mind.
That's a good video ... AND it's plastic Michael I subscribe to Tom Lipton's Youtube channel, almost certainly saw that video when it came out, and just filed the information away for a "rainy day" Guess it's raining today. However I have his book too and maybe it was in there also? I can't recall. I haven't been watching his videos recently as they're quite lengthy, but the guy is a mine of information and he's put me on to some great stuff. He always answers enquiries about questions or to confirm model numbers etc, so have spoken to him regularly either through the channel or direct messaging. Tom is a very nice guy. I subscribe to about 20-30 people's Youtube channels, though only watch the topics I'm interested in at the time. I don't rot my brain with television, but if I have time in the hotel rooms this is how I prefer to use it.
I think Tom explains the principles of direct indexing well. The only way to get 107 equally spaced divisions is to space each hole by 3.4 degrees (or whatever it was, I don't have my CAD program open now). However there is no requirement for all the holes to be on the same radius, only that they are the same angular distance apart. As you get closer to the hub of the index plate the resolution will reduce to the point where it may become a factor. There's no worm to divide the errors in the indexing plate and besides 53 is quite a small and workable plate as it is. Ray I think you will find the 54th hole will interfere with the first, that's why it needs to be offset on a third radius.
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21st August 2015 03:38 PM # ADSGoogle Adsense Advertisement
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21st August 2015, 03:41 PM #47Pink 10EE owner
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I have not actually read the thread as it is too long for my attention span, but I just thought up an idea for a quick indexer besides Pete's good idea of making one out of plastic...
Make up a suitable piece of round material... Put it on a mill with DRO... Drill the required number of holes... Put the round piece back on the lathe and turn down the OD until only half the holes remain.. deburr, then you have a "gear" with "teeth" to put a locking mechanism in..Light red, the colour of choice for the discerning man.
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21st August 2015, 03:54 PM #48SENIOR MEMBER
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21st August 2015, 06:55 PM #49Member
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Bob
You could make a simple dividing plate easily by turning a piece of MDF/Ali to a diameter of 170.227mm & then use a tape measure around the circumference to mark 5mm increments.
Regards
JohnQLast edited by JohnQ; 21st August 2015 at 06:56 PM. Reason: Spelling
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21st August 2015, 08:31 PM #50Philomath in training
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I was only using 54 as an upper bound on the space/ length needed
It works - it's just not elegant.
BC.jpg
Hmpf! It 'aint real machining if it doesn't make swarf!
Michael
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21st August 2015, 10:02 PM #51SENIOR MEMBER
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Michael, you can see that 54th hole is interfering. I guess in that regard it would work, but it's beyond not being elegant, and I certainly wouldn't do it. There is no real disadvantage to dropping that odd hole down to a third radius and getting him out the way.
Hmpf! It 'aint real machining if it doesn't make swarf!
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21st August 2015, 10:44 PM #52Philomath in training
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True. For a one off I'd probably risk it (maybe smaller holes, larger PCD to get some space). For a repeat job I'd probably do a third row - actually, if I had a third row in there I'd probably set the plate up with 35 or 36 holes per row. If you have to move the index pointer in another diameter, may as well make it useful.
Don't tell my better half - she loves that stuff ever since a trip to the US. She'd want me to print everything just for the aroma
Michael
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22nd August 2015, 09:15 AM #53.
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A probably insurmountable problem for me John would be the accurate marking of the increments and ensuring that the marks were uniform. The need for uniformity becomes apparent
when trying to centre the mark with a 20X microscope. The attached photo is of the finest line our printer at work can achieve. It is from the corner of the drawing I posted a photo of earlier. Fine to the naked eye......
DSC_4862 (Large).JPG
The "line" width is approximately 0.08mm or 0.003". Finer than anything I reckon I could achieve with any consistency 107 times.
Now some might question this need for accuracy. The exceptionally smooth* fine focus control features easily divisible 0.002mm graduations. The machining of a replacement gear needs to be accurate to maintain the smoothness. The scope's maximum magnification is 1000X with the present combination of oculars and objectives. A lack of smoothness at that magnification would be um.. undesirable.
Bob
* until it encounters the split.
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22nd August 2015, 10:00 AM #54SENIOR MEMBER
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Bob I always like the way you do things "right", and clearly this is no exception. However I can't help but wonder if you're not overly concerned about the accuracy of this part in regard the indexing. As an exercise you may want to calculate the angular difference in the gear teeth with an indexing error at the circumference of the indexing plate. I haven't done so, but will be extremely small.
The gear you are cutting won't be hobbed, therefore it won't be true involute and only an approximation. On the other hand it is nylon originally (and if smoothness is a concern, that's what I'd replace it with too), and is naturally somewhat pliable. It also naturally moves and changes shape slightly with differences in humidity. The bottom line is, in my opinion, the smoothness you seek won't be affected by indexing errors in your dividing plate of the magnitude we're talking about here.
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22nd August 2015, 03:28 PM #55GOLD MEMBER
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Given you shouldnt have to much trouble picking that line up within 0.04mm thats 0.0024mm!!
Though if you use your rotary table and take the 5 second error thats 0.00043mm
I really think plates are about speed and reducing errors than outright accuracy. Though at tooth 100 I think you'd be feeling the pressure
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22nd August 2015, 07:58 PM #56SENIOR MEMBER
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Would fine clockmakers tools be relevant ?
Hey,
Gotta admit some of the discussions over my head.
Have been wondering if the very fine tools used for clock and watchmaking might be useful for this fiddly small 107 tooth gear.
Ie this thing is a DIY version of an $8,000 dollar clockmakers gear cutter,
http://www.projectsinmetal.com/free-...r-clockmaking/
I guess it still comes back to the accuracy of the indexing wheels.
Bill
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22nd August 2015, 08:28 PM #57SENIOR MEMBER
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Just make one tiny segment of the wheel and keep swivelling it around ?
Woodworkers sometimes use jigs where a small distance between two things is used again and again to repeat a measurement.
https://www.google.com/search?q=fing...w=1440&bih=904
COuld a similar trick be done to extremely accurately make a section of the 107 tooth index wheel and then keep using it again and again ie only drill a few holes but do it as accurately as possible and use the same segment again and again instead of attempting to very accurately locate all 107 holes ;
ie see attached sketch
Bill
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22nd August 2015, 08:55 PM #58GOLD MEMBER
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Hi Bill,
Thats fine until you get to the last hole, the distance from it to the first hole will be a collection of 107 pitch errors +/- any random pitch error from the jig. Even an error of 0.001mm leaves you with a pitch error of 0.1mm. Now if in use the gear doesnt do a full rev...................
Stuart
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22nd August 2015, 08:59 PM #59Philomath in training
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In theory yes, but in practice because of the application it is unlikely to be satisfactory, simply because of the cumulative error that is possible (107 holes with the pitch out by say 1% means that you could possibly lose a complete hole. If that is on a PCD of say 150mm, 1% of pitch is 0.04mm which is probably around the clearance you have between a bush and pin/ marking device).
The best thing to use for laying out these holes is an analogue computing device - also known in this application as a dividing head (or as you linked to, a gear cutting engine). A digital device (digital rotary table/ CNC mill, printer, ...) would be the next best thing but depending on the graduations in the encoder will have varying amounts of error.
Laying out by hand or using a drafting package and pasting a plot onto a blank would work but would rely greatly on accurate work, paper not stretching/ distorting and probably at the end of the process, a dollop of luck. 3D printing would reduce the errors from systematic to random so would be better but it's also one of those effort vs. reward things - how much resource do you spend making one off tooling? Spend too little and potentially all your efforts will be wasted. Spend too much and you will have the result you want but the cost (especially time) may be more than is warranted.
Michael
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22nd August 2015, 09:06 PM #60
I've got some polycarbonate jobs to do on the mill tomorrow, I could knock out a 107 hole polycarbonate disk using PCD with 2mm hole size and 100 mm diameter.
100 * 3.142 = 314.2 314.2/107 = 2.936mm between holes centers on a single radius, so a 2mm drill should do the trick, If your indexing pin is 3mm then just make a tapered pin, say from 3 down to 1.8mm
I'd do it all in one setup, just drill the center hole at 2mm as well, and then you could center it on the lathe to bore out whatever center hole you want.
Ray
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