Gear cutters

[raysalParticipant @raysal]

About six months ago I bought a 32 DP no 5 gear cutter from RDG and also asked for the no 3. They were out of stock of the no 3. I wanted to learn gear cutting for building the Webster ic engine. I tried again yesterday and still no no 3 anywhere, even on the chinese sites. What has happend to the no 3, have they stopped producing them? any info appreciated

[raysalParticipant @raysal]

[JasonBModerator @jasonb]

Talking with Ketan the other week many of the Chinese factories including Sieg have been closed for a good part of this year so that is having a massive effect on the supply chain.

[Paul LousickParticipant @paullousick59116]

I don't cut gears but a quick search found cutters on a number of sites,Like this one.

**LINK**

[DC31kParticipant @dc31k]

Posted by Paul Lousick on 07/07/2022 10:20:44:

I don't cut gears but a quick search found cutters on a number of sites,Like this one.

I think his request came wth the unspoken proviso of 'reasonable price'. Over £100 for a single cutter does not, I think, meet that requirement.

It would be worth looking at overseas sources of 0.8 MOD cutters as they are likely close enough to work adequately (first one I found was just under £90 for a full set of 8 cutters).

[JasonBModerator @jasonb]

He also wants 14.5deg pa not the more common 20deg pa

[Thor 🇳🇴Participant @thor]

If you don't want to wait for RDG to get the No 3 cutter in stock you could try and make your own gear cutter. I have made a few myself from either silver steel or gauge plate – hardened and tempered. Mike's workshop has the tables with the dimensions needed.

Thor

[raysalParticipant @raysal]

Hi Thor no,

Although I have been a hobbist engineer for a few years my skills are quite basic, I have built only sterling engines and steam engines. I am probably pushing it skill wise building a Webster engine so trying to make my own cutters would be a nightmare but thanks anyway for having faith in me lol.

As DC31K mentions you can find them at £100 each but I can't go to those high prices. If I can't find a no 3 at the price RDG sells gear cutters for (£25)I will resort to buying the ready made gears. These are a reasonable price but I like the idea of trying to make the whole engine myself.

[DC31kParticipant @dc31k]

Posted by JasonB on 07/07/2022 10:45:53:

He also wants 14.5deg pa not the more common 20deg pa

Is there some existing feature of the engine that makes a particular PA necessary? If all the gears are being made, an option is to write off (or sell on) the cutter he has and invest in two new ones.

[JuddyParticipant @juddy]

Home and workshop Machinery normally have a lot of secondhand gear cutters at reasonable cost:

Miscellaneous | Home and Workshop Machinery

[Howard LewisParticipant @howardlewis46836]

If the gears are for an I C engine, the important thing is the ratio. (Presumably 2:1 )

Obviously, you don't want 10 DP gears but will it make too much difference if the 14.5 PA 32 DP gears are replaced by 20 PA 0.8 Mod gears, or some close equivalent?

Howard

[raysalParticipant @raysal]

I find it difficult to understand gear cutters but did wonder as DC31K mentions if there was another way arround this by selling the no 5 32DP and buy a matching pair of say 20 PA 0.8 mod gears to achive the 2:1 ratio.

I thank you all for your help and have decided I need to go back to studying the basics of gear cutters to see if the above way can be achieved. I must admit as I am so dumb on the subject it looks favourable now to buy ready made gears that I have the part numbers for.

Juddy, thanks for the heads up on the home and workshop machinery site, it looks a amazing site, I will certainly give them a try first.

[Martin ConnellyParticipant @martinconnelly55370]

The 14.5° PA causes slightly less pressure on the axles carrying the gears (trying to push the gears apart) compared to 20° PA but has a slightly weaker root on the teeth. If you can get 20° PA gear cutters they may be just as good for your purposes as I doubt there is going to be such a huge amount of power going through them that these factors need to be considered. Just make the gears match each other.

Martin C

[DC31kParticipant @dc31k]

Posted by raysal on 07/07/2022 17:26:48:

I thank you all for your help and have decided I need to go back to studying the basics of gear cutters to see if the above way can be achieved.

For the model you are to build, you are fortunate that the designer has specified 32 DP gears (and spaced the shafts on which the gears run accordingly). 32 DP are one of a few imperial specification gears for which the nearest standard metric specification gear is close enough to make no appreciable difference. In a way, it parallels using a 19mm spanner where a 3/4" one is needed or 5/16" where 8mm is strictly correct.

Even if you are to buy the gears it is worth exploring both options as one may be more economic than the other due to supply and demand.

[JasonBModerator @jasonb]

If you do decide to go down the 0.8MOD route then you just need to move the position of the cam's stub pivot 0.009" closer to the crankshaft. Though rather than measure it would be worth "depthing" the gears with a strip of fag paper or thin polythene between the teeth to give a little backlash. I've use 20 pa and 14.5 pa gears for engine timing so both will work just not both on the same engine

[Michael GilliganParticipant @michaelgilligan61133]

Raysal

It took a while to find my old post, but

If you want to appreciate ‘Pressure Angle’ have a look at the animation on this thread:

**LINK**

https://www.chiefdelphi.com/t/turning-down-the-od-of-a-gear/137417/22

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Gear cutters don't cut gears, they cut the spaces between the teeth"

Imperial cutters ( SOmetimes referred to as Brown and Sharpe cutters after one of the fist supplier ) are numbered from 1 to 8, with each number being suitable to cut a range of toothg counts, with 8 cutting 12 and 13T, and 1 being suitable to cut from 133t to a rack.

I think that cutters for Module gears are similarly numbered, but in the opposite sequence, so that 1 cuts small tooth counts and 8 the largest. If I am wrong in this, someone will correct the statement.

Ivan Law's book "Gears and Gear Cutting", No 17 in the Workshop Practice Series will tell you far far more than I can.

Howard

[raysalParticipant @raysal]

I made a electronic indexer a while back that works spot on. When I purchased the #5 gear cutter I cut quite a few equal toothed gears in brass for practice. If I had, had the #3 at the time I feel I would have cut the required Webster gears ok. I do understand gearing and ratios as I used to have to work out gearing when building Hotrods in the past. Where I am as I say "dumb" is I don't understand the maths and calculations for working out what gear cutter I need for a specific job. I also can't understand the swap-ability of different DPs, PAs, and module copared to DP. I am like the youtuber "Thunderdog" I am useless at maths, he however IMO does the best simple explanation to get the end result.

Howard I bought that book after watching Andrew from Leaning Turning recommended it. This is how I am going to play it after all your help. I will buy the gears for the Webster and meanwhile look out for the elusive #3 cutter while building it.

[Anonymous]

I'll second the book by Ivan Law. Good on the fundamentals of spur gears but weaker on more advanced types of gear. The maths isn't complicated, early secondary school level.

Which gear cutter to use for a spur gear is easy. For each cutter the range of teeth it wil cut is specified. Simply pick the cutter that covers the tooth count desired. The form of the cutter is exact for the lowest tooth count in the range and gets progressively less accurate as the tooth count increases. The errors are small and don't concern us in most ME applications.

Be aware that the numbering of cutters in the Module system is the the reverse of that in the DP system. So a number 1 cutter in Module will cut a gear of 12 or 13 teeth. In the DP system a number 8 cutter will cut a gear of 12 or 13 teeth.

Andrew

[raysalParticipant @raysal]

Andrew, After trying so hard to find the #3 32DP cutter I did think of going module instead after a suggestion on here of going 0.8 Mod, Then I realised I had bought a arbor to suit the DP gears with a 1" Bore. I don't think there are any MOD arbors with a 1" bore. I will just do as I said in the above post and buy the gears for now.

[raysalParticipant @raysal]

Thanks for that Andrew. Perhaps I am looking too much in to gear cutters and making it more complicated than I think. So you are saying it does not mater what DP or Module set of cutters I buy, I just pick the ones with the amount of teeth I need and that will achieve what I want. So in theory I can go on Ebay and just buy any set that comes up.? There are some cheap sets that I can buy off Ebay with a DP20 or DP16.

[Anonymous]

Posted by raysal on 08/07/2022 10:28:45:

…it does not mater what DP or Module set of cutters I buy…

No, that is incorrect. I have to go out now, syndicate meeting about our broken sailplane, but will try and explain in more detail later.

Andrew

[John HinkleyParticipant @johnhinkley26699]

I had a quick look at the pdf plans of what I presume to be the engine that you are building, but nowhere could I find a reference to the number of teeth on each gear, nor the distance between gear centres. Don't forget that, if you change from DP to MOD gears, there is little chance of the gear sets having the same centre to centre distance. Give us these details and we can possibly work out suitable MOD alternative pairs. I have a few sets of gear cutters and an arbor which you could borrow if a suitable combination can be found. I'm assuming that you reside in the UK as you have no profile.

John

[roy entwistleParticipant @royentwistle24699]

Raysal I don't know but having a different DP from drawings could alter the gear centres specified

Roy

[JasonBModerator @jasonb]

Don't be put off by the size of your arbor, I turned a simple bush so I can mount metric 22mm bore gear cutters and slitting saws on my imperial 1" arbor that just replaces one of the spacer rings. I'll take a picture a bit later.

 

Different DP won't alter the PCD (gear centers) as you simply alter the tooth count to suit. so 32DP 48/24T set as specified could be changed to 16DP 24/12 or 24DP 36/18, etc. Similar with MOD you would just pick a size and number of teeth to get the closest to the existing PCD. Just so happens 0.8MOD is very close to 32DP which make sit the easiest to change to with the small adjustment to pcd as I mentioned earlieror you could for this use get away with increasing the OD of the gears a bit and keep the same ctrs as they are so close (don't let Andrew catch me saying that)

John the part numbers for the gears give the clue to what they are both start with 32 which is the DP and end in 48 & 24 which is the tooth count There are two dimensions vertical and horizontal to the hole the cam gear pivot fits into on the frame drawing. Diagonal distance should be PCD

Edited By JasonB on 08/07/2022 16:44:45

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