Thread: 0.3 Module Gear Cutting Query

Originally Posted by aarggh

Hi Bob, if it's only split, could you just use some nylon glue to fix it, and enlarge the bore slightly to reduce pressure?

I don't know Aarggh. There may well be grease on the gears and grease might impregnate nylon ( ? ) creating an issue with adhesion. I need to pop the assembly apart for a reconnoitre. I didn't know that adhesives were available for nylon until your reply - http://www.loctiteproducts.com/p/epx...tic-Bonder.htm

A skim of the brass hub and gluing the gear would sure beat gear cutting. Gluing the gear onto the hub would probably help too.

Bob.

Originally Posted by Anorak Bob

I don't know Aarggh. There may well be grease on the gears and grease might impregnate nylon ( ? ) creating an issue with adhesion. I need to pop the assembly apart for a reconnoitre. I didn't know that adhesives were available for nylon until your reply - http://www.loctiteproducts.com/p/epx...tic-Bonder.htm

A skim of the brass hub and gluing the gear would sure beat gear cutting. Gluing the gear onto the hub would probably help too.

Bob.

Yeah, sometimes I think the simplest solutions are the best, the adhesives nowadays are pretty good so with a thin support glued on top if possible it should last quite some time more.

cheers, Ian

Now if the simplest solution doesn't work I'll be back to gear cutting. Or maybe leaning on either Pete or Michael for a favour.

Michael will soon have the facility to cut the gear thanks to Chris' link to the cutters on eBay but I'm already heavily indebted favourwise to Michael and I'm thinking I really need to have a go myself before I increase the debt.

Pete's offer of a printed division plate is very appealing but the 107* holes required might possibly be too much for the plastic to cope with. Direct indexing might also expose the fragility of the plastic. This photo better illustrates the 110mm diameter plate with its deep vee-ed 60 divisions and the indexing pawl -

023%20(Large).JPG

The indexing pointer in the arm could be replaced with something that facilited a simpler printing? What do you think Pete?

* Martine's calculations -
360 degrees / 107 = 3.3644859813084112149532710280374 degrees per division.

On 6 degree division plate = approx 0.566 of a full revolution.
= hole number 60 of 107.

Hole sequence from there on: 60 holes further.
= rotation number x 60 mod (107)
( ‘mod’ being remainder of holes after dividing by 107.)

BT

Originally Posted by Anorak Bob

Michael will soon have the facility to cut the gear thanks to Chris' link to the cutters on eBay but I'm already heavily indebted favourwise to Michael and I'm thinking I really need to have a go myself before I increase the debt.

I think the last think I did for you was spend some of your cash on a vice. I hardly think that spending someone else's money counts as a favour .

Michael
(Yes, there may have a been a few other little things but if I can't remember them why should you? - and then there is the principle of paying forward?)

Originally Posted by Anorak Bob

Now if the simplest solution doesn't work I'll be back to gear cutting. Or maybe leaning on either Pete or Michael for a favour.

Michael will soon have the facility to cut the gear thanks to Chris' link to the cutters on eBay but I'm already heavily indebted favourwise to Michael and I'm thinking I really need to have a go myself before I increase the debt.

Pete's offer of a printed division plate is very appealling but the 107* holes required might possibly be too much for the plastic to cope with. Direct indexing might also expose the fragility of the plastic. This photo better illustrates the 110mm diameter plate with its deep vee-ed 60 divisions and the indexing pawl -

The indexing pointer in the arm could be replaced with something that facilited a simpler printing? What do you think Pete?

* Martine's calculations -
360 degrees / 107 = 3.3644859813084112149532710280374 degrees per division.

On 6 degree division plate = approx 0.566 of a full revolution.
= hole number 60 of 107.

Hole sequence from there on: 60 holes further.
= rotation number x 60 mod (107)
( ‘mod’ being remainder of holes after dividing by 107.)

BT

G'day Bob, it's seriously no effort to print this off for you, and I think you underestimate both the accuracy and strength of the finished prints in plastic. At the BCD of the indexing plate, the minor errors in the printed plate's dimensions I think would be so small when considering the diameter of this gear, and also the application, that I think it would be immeasurable. I typically only use 20-30% infill so as to save plastic, but there is no great strength required in an indexing plate, it's only to locate the pin and then the spindle on the dividing head is locked. The issue is more with wear, but for something like this I can't imagine it will be an issue at all, not unless you're thinking of doing this as a side-business Anyway, I think it would be worth a try, and there's no great investment of time and money if it doesn't work. Obviously a CNCed metal version would be better, but failing that this is what I would use if I were faced with the same problem. You could always do a spreadsheet with X + Y coordinates if you really wanted to self-cater, but I fear the potential for screw up would be extremely high.

I didn't follow your calculations, but if you wanted to direct index it I would suggest if it's possible to do it with a pin at various radii rather than the notched design you showed, the pin would be much better. You still direct index, but just set up a pin to locate in the plate's holes, even if the pin is just a temporary setup. By doing it that way you can make the plate much smaller as described above by using 3 different radii on which to position the holes so they're not overlapping each other. I'd think 107 notches around the perimeter would require an overly large plate, possibly so large that it would foul the table. However I'm only guessing at that without dimensions. Yesterday I did some rough modelling, just to make sure the concept was sound, and I couldn't see any problems with doing it this way. Not knowing the size of your plates, I just threw in a 150 mm plate and 4 mm indexing pin, and it looks like all the holes will fit without any problems. You should be able to test it in the AutoCAD you use and come up with accurate dimensions instead of my arbitrary figures.

Originally Posted by Pete F

... if you wanted to direct index it I would suggest if it's possible to do it with a pin at various radii rather than the notched design you showed, the pin would be much better. You still direct index, but just set up a pin to locate in the plate's holes, even if the pin is just a temporary setup. By doing it that way you can make the plate much smaller as described above by using 3 different radii on which to position the holes so they're not overlapping each other. I'd think 107 notches around the perimeter would require an overly large plate, possibly so large that it would foul the table. However I'm only guessing at that without dimensions. Yesterday I did some rough modelling, just to make sure the concept was sound, and I couldn't see any problems with doing it this way. Not knowing the size of your plates, I just threw in a 150 mm plate and 4 mm indexing pin, and it looks like all the holes will fit without any problems. You should be able to test it in the AutoCAD you use and come up with accurate dimensions instead of my arbitrary figures.

G'day Pete
Bob's existing plate is 110mm diameter and it does not look like it could get much bigger in diameter. To avoid having to change the indexing on his head too much, would it be possible to print out a disc with holes on the edge?
54x3mm holes with 3mm between them is a diameter of 103mm, so two rows of holes would just about do it I think. An indexing pin of 3mm diameter should be simple enough to install in that DH and Bob's your... er... well... mate! (the other possibility is a 110mm diameter notched wheel - if the notches were around 3mm peak to peak that would serve as well. Bit like the current one but far finer)

I must confess to being one of those who probably underestimate the strength and accuracy of plastic parts made this way. One day I might have to get you to make up a couple of test patterns for me to check the repeatability of build, surface finish and strength. I'll probably be pleasantly surprised (But I do reserve the right to grouse about this new way of doing things anyway)

Michael

Originally Posted by Pete F

G'day Bob, it's seriously no effort to print this off for you, and I think you underestimate both the accuracy and strength of the finished prints in plastic. At the BCD of the indexing plate, the minor errors in the printed plate's dimensions I think would be so small when considering the diameter of this gear, and also the application, that I think it would be immeasurable. I typically only use 20-30% infill so as to save plastic, but there is no great strength required in an indexing plate, it's only to locate the pin and then the spindle on the dividing head is locked. The issue is more with wear, but for something like this I can't imagine it will be an issue at all, not unless you're thinking of doing this as a side-business Anyway, I think it would be worth a try, and there's no great investment of time and money if it doesn't work. Obviously a CNCed metal version would be better, but failing that this is what I would use if I were faced with the same problem. You could always do a spreadsheet with X + Y coordinates if you really wanted to self-cater, but I fear the potential for screw up would be extremely high.

I didn't follow your calculations, but if you wanted to direct index it I would suggest if it's possible to do it with a pin at various radii rather than the notched design you showed, the pin would be much better. You still direct index, but just set up a pin to locate in the plate's holes, even if the pin is just a temporary setup. By doing it that way you can make the plate much smaller as described above by using 3 different radii on which to position the holes so they're not overlapping each other. I'd think 107 notches around the perimeter would require an overly large plate, possibly so large that it would foul the table. However I'm only guessing at that without dimensions. Yesterday I did some rough modelling, just to make sure the concept was sound, and I couldn't see any problems with doing it this way. Not knowing the size of your plates, I just threw in a 150 mm plate and 4 mm indexing pin, and it looks like all the holes will fit without any problems. You should be able to test it in the AutoCAD you use and come up with accurate dimensions instead of my arbitrary figures.

AutoCAD hey Pete.

IMG_4838 (Large).JPG

I reckon I could enlarge the dividing plate a touch, depends on the slot length in the indexing arm. My concern about multiple circles is a loss of registration of the indexing pin. From memory, the holes are about 2.5mm in diameter. I will measure things tomorrow and snap a photo or two.

Bob.

Michael printing holes on the edge probably wouldn't result in them being very clean and round. Sometimes I'm however surprised with how well horizontally orientated holes work out though. The issue is that FDM style printers can't build a feature in air. So in other words you can't have an overhang as it needs to build from the build plate up. Holes are often ok, as it gradually leads into the hole, and back again, and it typically handles that ok, especially smaller holes, but this isn't ideal. There are ways to get around this, for example support can be incorporated into the part in printing it, and this support is then snapped away after the part is completed. The slicer (the CAM part of the equation) designers are very clever with support, and it comes away almost without leaving a trace. I have no idea how they do it, just one of those tricks of engineering known only to the software designers I guess.

Having the holes on edge would be a good way to maximise the circumference, however apart from the above it would be inefficient in terms or material use. While the plastic isn't expensive, it's not free either, but more the point is that it adds a lot to the build time. The biggest issue with this type of manufacturing is that it is VERY slow. I normally use 0.2 mm layer heights, but that photo I posted above of Marvin was 0.1 mm layer height. A thick indexing plate could take hours to print if very high (relatively speaking) resolution is required. I try to always minimise the physical size of something if i can when designing it to reduce that build time as much as possible.

Sure, email me a concept of what you want printed and I'll get something over to you. There are plenty of test models available, but it's probably better if you sent something that you imagined in your own mind first, and then can see how the finished product looks like. Don't get me wrong, I'm certainly not holding this up to be some panacea or miracle manufacturing technique, it's far from it. Indeed it's best to continue to think of it as a rapid prototyping technique; how it all started in the first place. However many times people are conditioned to think in terms of conventional machining and feel that everything needs to be accurate to within 10 micron and strong enough to support a jumbo jet! The reality is that often it only needs to be strong and accurate enough to fulfil the purpose, anything more is wasteful in terms of engineering. There are many applications where we may have previously thought in metal, and if it were a commercial product that would be the appropriate material, but for a single use it may be complete overkill. Likewise for accuracy. I have a Hercus dividing plate where the accuracy of the holes is a joke. They are all over the shop and that can clearly be seen by eye. Admittedly the accuracy is improved in practice due to the dividing nature of the head, but in the case of cutting a nylon gear I suspect that a 3D printed plate would be accurate enough. No guarantees however, but if not there's not been a lot invested in trying. On that note I just did a search to see if anyone has done this before, and indeed just found this http://www.thingiverse.com/thing:15712 No idea how it worked out for the person, but at least we're not the first to try it!

Bob, I don't follow what you mean by the loss of registration. The pin normally slides in a slot, so moving from one diameter to another shouldn't make any difference. You just slide it in or out as required and continue to index the missing holes. I'll quickly throw in a model for 110 mm and see how much room we have to play with 2.5 mm holes.

Edit: I was just fiddling with different diameters Bob, and you would probably need to be up around 150 mm to be able to do 107 holes in one circle. That provides just under 2 mm between holes, even that it a bit tight in my opinion, especially for this type of construction. Often a 3D printed part is little more than a "casting" or similar that will need further work before it's ready for use. You will almost certainly for example need to run a drill bit or reamer through the holes to size them properly before use. i have never really worried about accurately calibrating my printer for size, as that is not normally critical in what I use it for. If it is, I re-work the print

Originally Posted by Michael G

54x3mm holes with 3mm between them is a diameter of 103mm, so two rows of holes would just about do it I think.

Oh BTW Michael, I don't think this will work in the way I think you're imagining. You can't put in 2 rows of 54 and just leave one out at the end to get 107.

Bob if your existing dividing head doesn't prove suitable perhaps you have something else that may be used? Because the plate is direct indexing any spindle you have would be suitable, and the worm is not required. So a rotary table freewheeling, a spindexer, lathe (if you then had the facilities to mill the actual gear on your lathe, otherwise you could slot it using the carriage ... if you're patient enough. It is however only plastic or brass so would go relatively quickly that way), or any form of spindle will do. All you need to do is have the ability to mount the index disk on it, be able to lock it, and be able to mount an indexing pin on a slot somewhere. With that in mind it may be able to open up other possibilities.

Making an indexing plate using the PCD program on the DRO, I would enter the outer diameter and program for 107 holes, then go around once skipping every second hole, then re-enter with same center and zero co-ordinates but decrease the diameter by 6mm and then do another circuit picking up the other holes. So you would have 54 holes on the outer circle and 53 on the inner circle.

The outer circle 110mm diameter, spacing between 54 holes would be 6.4
The inner circle 104mm diameter, spacing between 53 holes would be 6.2

So you could make the holes 3 mm or whatever suits the indexing.

Another way would be to enter the outer diameter and 54 holes, then calculate the offset start for the inner circle and 53 holes?

Ray

Originally Posted by RayG

Making an indexing plate using the PCD program on the DRO, I would enter the outer diameter and program for 107 holes, then go around once skipping every second hole, then re-enter with same center and zero co-ordinates but decrease the diameter by 6mm and then do another circuit picking up the other holes. So you would have 54 holes on the outer circle and 53 on the inner circle.

The outer circle 110mm diameter, spacing between 54 holes would be 6.4
The inner circle 104mm diameter, spacing between 53 holes would be 6.2

So you could make the holes 3 mm or whatever suits the indexing.

Another way would be to enter the outer diameter and 54 holes, then calculate the offset start for the inner circle and 53 holes?

Ray

Except it wont work like that

I think you'll find the first and last holes are on one circle, one pitch apart.(though I havent got my head around the maths just yet )

Stuart

Originally Posted by Pete F

Oh BTW Michael, I don't think this will work in the way I think you're imagining. You can't put in 2 rows of 54 and just leave one out at the end to get 107.

Bob if your existing dividing head doesn't prove suitable perhaps you have something else that may be used? Because the plate is direct indexing any spindle you have would be suitable, and the worm is not required. So a rotary table freewheeling, a spindexer, lathe (if you then had the facilities to mill the actual gear on your lathe, otherwise you could slot it using the carriage ... if you're patient enough. It is however only plastic or brass so would go relatively quickly that way), or any form of spindle will do. All you need to do is have the ability to mount the index disk on it, be able to lock it, and be able to mount an indexing pin on a slot somewhere. With that in mind it may be able to open up other possibilities.

How's this Pete?

DSC_4858 (Large).JPG DSC_4860 (Large).JPG

Whilst the photos might suggest otherwise, my intention would be to machine a rigid support for the indexing arm, which would be mounted at spindle centre height with the facility to slide radially to pick up the three rows of holes. Bob "Krisfarm" very kindly sent me a link to a Tom Lipton YouTube clip showing just what we are discussing -https://www.youtube.com/watch?v=m_VO9uRigQ8

Originally Posted by Stustoys

Except it wont work like that

I think you'll find the first and last holes are on one circle, one pitch apart.(though I havent got my head around the maths just yet )

Stuart

You are correct, ( as usual ) all the odd holes will be on the outer circle, and all the even numbers on the inner circle. So the last hole on the outer circle would have to be 105, then a third circle for the last hole number 107.

PS. That Ox video is spot on.

Originally Posted by RayG

You are correct, ( as usual ) all the odd holes will be on the outer circle, and all the even numbers on the inner circle. So the last hole on the outer circle would have to be 105, then a third circle for the last hole number 107.

Drawing paper stuck to MDF is looking good

Stuart