Gear Cutters

[mklotz]

Brian,

If you download my DIVHEAD archive, one of the included programs is DPLATES. It will, given your DH gear ratio, tell you what plates you need to get all divisions up to an input value 'N'. The primary program in that archive, will, given your ratio and available hole plates, tell you how many turns and holes are needed to do any of the divisions possible with your equipment.

 

[lensman57]

I am considering purchasing a set of gear cutters for use when building model engines, etcetera. I know that members on this forum have them---I think Tel and Chuck do. What size would you knowledgeable people recommend? I feel kind of dumb, as I'm not even 100% sure what these things are called. I just did a search for "gear cutters" on littlemachineshop. com and nothing came up. ---Brian

Hi Brian,

I too am about to start the build of my first IC engine that requires two 32 DP gears of 24T and 48T. Have been looking around for the cutters and either The correct cutters are not available on the eBay or the ones from the tool shops are just crazy expensive, £136.00 plus 20% tax and postage for a32 DP no3 cutter.
I have decided to make my own cutting hobb and found this little calculator for the gears.
http://www.doov.com/cgi-bin/tgc_spurgear.cgi

Just enter 3 simple data set and the calculator will give you the gear data and you can use that to machine the hobb, of course you need to make a simple grooving tool of 40 Degree included and also you need a rotary table of some sort to rotate the hobb.
For the 32 DP 24T that I am looking for the the grooves on the hobb should be 0.0982 apart, which is roughly the equivalent of the circular pitch value and I am sure if you added the values of the whole depth and the clearance value you get the depth of cut for the grooves, I think at least 5 grooves may be required, there is also this link in German for making the cutter but the photos are very clear, so I hope this helps, well I am going to have a crack at it and see what happenes.

http://www.metallmodellbau.de/GEAR-CUTTING.php

Regards,

A.G

 

[Brian Rupnow]

While doing a web search for explanation of how to use my divider plates, darned if I didn't find this thread which I started in June of 2010.
http://www.homemodelenginemachinist.com/index.php?topic=9695.0

 

[Maryak]

A lot of people think that having those plates will give you all numbers. Nothing is ever that simple, prime numbers are usually the ones unobtainable.
John

How true. I did find, (after much trial and error), that it is possible to compound index on a rotary table. It is not easy and a pencil and paper to keep track of how many holes in which circle helps not to lose you place.

Why did I do it.........I needed a 127 tooth gear to cut imperial threads on a metric machine.

Attached is a spreadsheet for a 90:1 ratio table which may be of use.

Best Regards
Bob

View attachment IndexRT.xls

 

[Brian Rupnow]

Thanks Maryak.---I'm trying to get my head around this divider plate business, and its slowly coming into focus.---Brian

 

[Maryak]

Brian,

Your welcome. Just one thing to remember and Marv has already mentioned it but it's worth saying again.

e.g. where the spreadsheet says No of holes = X, let X = 14 then the no. of holes between the 2 brass dividing leaves = X+1, 15; because the plunger is located in hole 1 and you need to advance 14 holes.

Best Regards
Bob

 

[hobby]

All his calculations are incorrect, since when has Pi been 3.4146 ?

John S.

I post this with all due respect, to John,
But I feel this needs to be made clear for others reading this thread.

I was watching the tape by "jose Rod." "making gears", and he used the value of "3.14" as the pi. in the equations twice.

If he used the other wrong value, later on, it was only a human error during his film production, probably due to having to keep talking and interest peeked for the viewers,

For others who may come to read this thread,
Please note, that the gentleman in the video, is indeed knowledgeable of using the right values, in the equations, and is very much capable of producing accurate results in his workmanship, in this case making gears, as well as his other machining projects.

 

[tel]

I too am about to start the build of my first IC engine that requires two 32 DP gears of 24T and 48T. Have been looking around for the cutters and either The correct cutters are not available on the eBay or the ones from the tool shops are just crazy expensive, £136.00 plus 20% tax and postage for a32 DP no3 cutter.
I have decided to make my own cutting hobb and found this little calculator for the gears.

30/60 in 40dp will put you in the same place.

RDG are pretty reasonable with their cutters.

http://www.rdgtools.co.uk/cgi-bin/ss000001.pl?page=search&SS=gear+cutter&search.x=10&search.y=8&PR=-1&TB=A

 

[Brian Rupnow]

Today my order from Travers showed up. I have learned thru experience that when purchasing thru mail order, a good close IMMEDIATE inspection is usualy a good idea.---And sure enough, everything looks good---EXCEPT #5 gear cutter, which is clearly marked 20 degrees instead of 14.5 degrees like all the rest of them. I will be speaking with the Travers people tomorrow morning. The overall quality looks quite good. I'm not sure about the arbor I bought, to the tune of $130.00, hoping I would be able to turn the 3/4" shank down to 1/2" which is the largest diameter my MT2 mill spindle will accept. It appears to be harder than the devils horn, but I'll take it to the factory where I am presently consulting and see if a new carbide in a BIG lathe will touch it.

 

[Brian Rupnow]

I spoke to the Travers people today, and they said that they would put a replacement cutter in the mail forthwith, and that they would fax me Fedex authorization to return the number 5 gear. I will let you know how that works out!!! I decided to make a 20 tooth gear, like the one in Hobbynut's video. Next, I got my divider plates out for a look and see that they are all the wrong number of holes for what I need. One has 15, 16, 17, 18, 19, and 20 holes. One has 21, 23, 27, 29, 31, and 33 holes. one has 37, 39, 41, 43, 47, and 49 holes. The charts that came with my rotary table make reference to an "A" plate with 26, 28, 30, 32, 34, 37, 38, 39, 41, 43, 44, 46, 47, 49, 51, 53, 57, and 59 holes, and to a "B" plate with 61, 63, 67, 69, 71, 73, 77, 79, 81, 83, 87, 89, 91, 93, 97, and 99 holes. My chart says that to make a 20 tooth gear, I need to use a divider plate with either 26 or 28 holes, which I don't have. The probability that BusyBee will be able to get these divider plates for me are probably slim to none, or they wouldn't have sold me the cheesy made in India divider plates which I had to modify to get the damned things to fit my rotary table.---HOWEVER--Another set of paperwork which I downloaded off the web for a 90:1 ratio rotary table made by MiniTech of California informs me that I can use a plate with 20 holes and do 4 10/20 of a turn. Let me see now, 360 degrees divided by 90=4 degrees for each turn of my handle. Half a turn of my handle or 10/20 should get me 2 degrees. In a 20 tooth gear, 360 divided by 20 =18 degrees. SO----4 1/2 turns of my handle should get me 4.5x4=18 degrees, so that sounds about right to me. Tell me guys, since my gears will be made of either aluminum or brass, can I take a full depth (.0899") cut each time? I have read about "gashing" the gear blank with a slitting saw to almost full tooth depth before even starting to use an involute cutter such as I have purchased, but i don't know if that applies to gears this small or not (I hope not)---Perhaps it only applies to steel gears or larger gears--does anybody know?

 

[mklotz]

Brian,

The way you determine table crank revolutions is:

Crank revs = Gear ratio / number of divisions

In your case the ratio is 90 and you want 20 divisions so...

90/20 = 4 & 10/20 = 4 & 1/2

just as you calculated.

You can get the half turn of the table by using the graduations on the handle (if they exist) or using half the holes on any hole circle that has an even number of holes, e.g.:

8 holes on the 16 hole plate
or
9 on the 18
or
10 on the 20

Save yourself more confusion. Download my DIVHEAD archive and learn to use the program therein.

 

[Brian Rupnow]

Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system. I did read the bit where you tell folks to right click on properties in the .exe file and select "program" and uncheck "close on exit", but it didn't work for me.---Brian

 

[gbritnell]

Hi Brian,
When cutting with an involute cutter in brass or aluminum it's not necessary to gash the material first. If you had a rigid machine like a Bridgeport you could take the cut in one pass but I still prefer to make 2 passes, one at about .075 and then to full depth. Another thing to keep in mind is to conventional cut. Here again if your machine lead screw is tight you could climb cut but it's not worth the chance. Generally I climb cut my finish cuts but with a cutter the diameter of an involute cutter you have quite a bit of leverage so stick with the conventional cut.
gbritnell

 

[Foozer]

Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system..---Brian

I use DosBox to run Marv's programs under linux. IIRC it will also work under the 64 bit win system

Robert

 

[Brian Rupnow]

Based on a little more research, I'm not as hard done by as I had supposed. I have went through the sheet I downloaded off the net from MiniTech in California and with my three nasty plates from India I am able to make most gears up to 100 teeth, the exceptions being 28, 44, 51, 52, 53, 56, 59, 61, 64, 67, 68, 71, 73, 76, 77, 79, 83, 84, 85, 88, 89, 91, 92, and 97 tooth gears. I'm not certain of the reasons for this, but I'm sure its something mathematically based. I can probably live with this, and if I find that I can not, I will persue it farther at that time. From what I have read, it seems that one of the gear cutters I bought is used to cut a rack. Although I know what a rack is, I'm not sure why only one of the gear cutters would be used to cut a rack, and not all of them, depending on what gear the rack was interacting with. I don't fully understand this, and since there is no explanation with the gear cutters, I may have totally misinterpreted what I read. If anyone can shed some light on this rack business, please let me know.
So----If I am understanding things correctly, first I have to determine what gears I want to cut (as in "how many teeth"). Then I have to search through the various cutters untill I find one that says it is used to cut a gear with that many teeth, then I have to look through my chart from MiniTech and determine whether or not I have a divider plate that will allow that many divisions. If I pass all these obstacles, then I can mathematicaly determine the o.d. of the gear so I know what size I have to turn my gear blank to in the lathe, and what my depth of cut will be. Since the machinist at work didn't have time to modify my arbor shank this week, I will probably spend this weekend determining what gears I want to cut,yada, yada, yada and make up a couple of blanks from brass or aluminum. I can probably even find some reference to what the pitch diameters of these gears will work out to, so that I can determine the correct center distance for the gears to mesh properly. WOW!!! Gear making is a lot of work, and I haven't even started yet!!!

 

[cfellows]

Brian, the cutter that is used on any given gear (or rack) is not based on the gear it interacts with. Rather, just the gear, or rack you are cutting regardless of what it's interacting with.

Pitch diameter is determined by dividing the number of teeth in the gear by the DP, in your case, 24. So, a gear with 24 teeth has pitch diameter of 1", 36 teeth would have a pitch diameter of 1.5", etc.

To get the overall diameter of your gear blank, you add the reciprocal of your DP X 2. So the reciprocal of 24 is 1/24 which equals 0.0416. Multiply this by 2 = .0832. Add this number to your pitch diameter. So, the OD of a 24 tooth gear would be 1" + .0832 = 1.0832.

Your tooth depth the reciprocal of 24 * 2 + about .006" or so for clearance. This would make the tooth depth .0832 + .006" or maybe round up to .090".

Chuck

 

[Brian Rupnow]

Now here is something really interesting. The "A" and "B" plates which I alluded to in an earlier post, (The plates I DIDN'T get), will make all of the gears which my 3 "India" plates won't. However there are no "part turns" called for. The divider plates actually have the same number of holes as the gear teeth.

 

[mklotz]

Thanks Marv. I did download your gearspur and divhead programs, but it gives me a message that it will not run on my 64 bit XP Windoze system. I did read the bit where you tell folks to right click on properties in the .exe file and select "program" and uncheck "close on exit", but it didn't work for me.---Brian

Brian,

DosBox is the tool of choice to run my programs on 64 bit systems. I've proved it out on my wife's Win 77 laptop so that statement is supported by fact.

GEARSPUR will automatically tell you which number cutter you need to use to make the gear.

GEAR will calculate center-to-center spacing although you don't really need a program for that. It's nothing more than the average of the pitch circle diameters of the two gears.

 

[mklotz]

Brian,

With a 90:1 gear ratio, here are all the hole plates one would need to do all the divisions up through one hundred. Using DPLATES, we have:

Hole plates required for all divisions up to 100
9,10,26,28,29,31,32,34,37,38,41,43,44,46,47,49,53,59,61,67,71,73,77,79,83,89,91,97

Not that this is a minimum hole count list - least work if making one's own plates. Plates with integer multiples of the given numbers could be used in lieu of the indicated numbers. For example, an 18 or 27 hole plate would allow one to divide a crank turn into ninths - 1 hole on a 9 hole plate is the same as 2 holes on an 18 hole plate or 3 on a 27.

 

[Brian Rupnow]

Now I'm really feeling dumb!! I downloaded Dosbox to try and open Marvs programs, but I don't know how to use it. Without being able to use Dosbox, how do I know which gear I should use to cut a given number of teeth? I'm sure this info has to be available somewhere other than Marv's program.---and Marv, thank you for trying to help me. I know your intentions are good, and I'm sure if you were here you could probably show me in 2 minutes, but I have never use Dos for anything. I didn't start to mess with computers until I was 50 years old, and have only ever used windows based programs.