Involute Gear Cutters

a41capt · Oct 28, 2024

I’m a new kid when it comes to cutting gears, and short of trying to make my own single point cutter, I thought I’d bite the bullet and buy a set of involute cutters.

My question to the group, from a model engineering standpoint, which DP set makes the most sense and provides the best range for the gears I might cut on model sized engines? In the past, I’ve purchased gears for my Kitchen Sink Engine and Webster, but that’s kinda like cheating!

Any-who, what’s the consensus of opinion, DP16, DP24, or?

Thanks in advance,
John W

Charles Lamont · Oct 29, 2024

This is largely a "how long is a piece of string?" question. A model engine that requires gears could be anything from say about 3cc enclosed crankcase petrol engine, which might want 40DP or even finer, to a half-size traction engine which might want something like 2DP on the final drive.

Think of the range of diameters of pinion you might want to cut. They will need to have a minimum around 16 teeth for a reasonable appearance in most applications.

Rdean33422 · Oct 29, 2024

I have found that my Module 1 cutters get the most use and are usually less expensive.

Ray

stevehuckss396 · Oct 29, 2024

Buy cutters as you need them. They are like drill bits in an index. You never use half of them. After many years of building models I think I have 8 or 9 cutters instead of 3 complete sets. Also if you buy specific cutters you can spend a little more to up the quality.

pileskis · Oct 29, 2024

stevehuckss396 said:
Buy cutters as you need them. They are like drill bits in an index. You never use half of them. After many years of building models I think I have 8 or 9 cutters instead of 3 complete sets. Also if you buy specific cutters you can spend a little more to up the quality.

Steve- I agree. Question is, who/where has reasonably priced good quality cutters?
US based?
Thanks, Sid

djc · Oct 29, 2024

Another way to consider the issue is to gen up on what size/specification/DP gears various workshop objects use. That might give you an indication of the relationship between scale/size and DP.

A standard mini lathe generally uses MOD 1 change gears. That is the same as 25.4 DP.

A Southbend lathe uses (I think) 18 DP. A Clausing/Colchester Bantam uses 16DP.

You could look at the sprockets on the bike in your picture. Count the teeth and roughly measure the OD. Work out the equivalent DP. Clearly, it will be too big for any model, but gives you another data point with which to calibrate your brain.

a41capt · Oct 29, 2024

Charles Lamont said:
This is largely a "how long is a piece of string?" question. A model engine that requires gears could be anything from say about 3cc enclosed crankcase petrol engine, which might want 40DP or even finer, to a half-size traction engine which might want something like 2DP on the final drive.

Think of the range of diameters of pinion you might want to cut. They will need to have a minimum around 16 teeth for a reasonable appearance in most applications.

Excellent example Charles, thank you! I have some more thinking to do, that’s for sure.

John W

a41capt · Oct 29, 2024

stevehuckss396 said:
Buy cutters as you need them. They are like drill bits in an index. You never use half of them. After many years of building models I think I have 8 or 9 cutters instead of 3 complete sets. Also if you buy specific cutters you can spend a little more to up the quality.

Not a bad option, it looks like an application by application purchase.

Thanks Steve!
John W

a41capt · Oct 29, 2024

djc said:
Another way to consider the issue is to gen up on what size/specification/DP gears various workshop objects use. That might give you an indication of the relationship between scale/size and DP.

A standard mini lathe generally uses MOD 1 change gears. That is the same as 25.4 DP.

A Southbend lathe uses (I think) 18 DP. A Clausing/Colchester Bantam uses 16DP.

You could look at the sprockets on the bike in your picture. Count the teeth and roughly measure the OD. Work out the equivalent DP. Clearly, it will be too big for any model, but gives you another data point with which to calibrate your brain.

Excellent thoughts. I have an Enco 10X18 (metric of course), a 13X39 Combo machine (also metric), and my trusty Atlas Clausing 12X36. Comparing these three against my gear needs for say Phillip Duclos “Odds and Ends” engine (32dp), that’s a wide ranging set of prospects!

Thanks for the insight,
John W

a41capt · Oct 29, 2024

Rdean33422 said:
I have found that my Module 1 cutters get the most use and are usually less expensive.

Ray

As many of my plans call for a DP sizing, Mod cutters usually don’t cross close enough to fit those plans. However, I have a decent app called Gear Lab on my iPad and it does allow for conversion of a sort, and even gives me adjusted center to center axle distances if I need to make that change.

Thanks Ray, I will consider buying a Mod 1 set (or pair) to fit my needs and perhaps just make plans adjustments as needed for axle distance.

John W

stevehuckss396 · Oct 29, 2024

pileskis said:
Steve- I agree. Question is, who/where has reasonably priced good quality cutters?
US based?
Thanks, Sid

I live less than a mile from KBC tool so thats usually where I look first. They are a bit more but no shipping so sometimes it works out. I also go to Victor Machine for cutters and non-standard taps and dies. They have a ton of stuff but hit or miss on the quality. They do say where the country of origin is. I try to stick with USA, Japan, Poland but have taken a chance on others when left no choice.

rklopp · Oct 29, 2024

The last ones I bought from Victor were measured with a micrometer, marked with a chalk, and cut with an axe. They were utter garbage, for which Victor quickly refunded my money without me having to send the cutters back. I've bought good ones from Toolmex (aka Bison chuck maker) directly, and what turned out to be Toolmex cutters from McMaster-Carr, for about the same price. The prices were not much higher than Victor's prices for junk.

stevehuckss396 · Oct 29, 2024

Yep but I have purchased some great quality stuff from Victor. Just check the country of origin. Like I said, hit or miss.

djc · Oct 30, 2024

a41capt said:
...Mod cutters usually don’t cross close enough to fit those plans.

I think that gear cutters, for all practical purposes, intersect at 32DP or 0.8 MOD. For hobby purposes, providing the pressure angle is the same, they are effectively interchangable.

That would give you a larger market from which to purchase individual cutters* and would mean you did not have to redo any drawings or recalculate any shaft spacings.

* be wary that MOD cutters are sometimes numbered the opposite way to DP, so pay attention to the actual tooth range engraved on the cutter, not just the given cutter number.

sarel · Oct 31, 2024

You can also make a rack form multi-tooth cutter to cut the gears. The advantage is that you can make different ones for the different DPs and Module. See article Gear cutting with a rack form multi-tooth cutter © Tony Jeffree 2008

Jasonb · Oct 31, 2024

As DJC says I have found that 32DP crops up a lot both on UK and US designs for the type of engine we see modeled here. Or 0.8MOD if you prefer to work in metric will give near enough the same PCD so existing castings can be used without having the camshaft gear at a a noticably odd position in it's boss.

But I have built models with gears ranging from 6DP to 0.5MOD so look at a few engines you may want to build in the future and see what gear size they use and make your purchase accordingly.

Sid, Last pair of cutters I bought were from Ali Express and they worked fine, shown below the 0.7MOD 25/50 pair. I have also used the RDG ones in the past which are OK.

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