What size gear cutter for gear

[David George 1Participant @davidgeorge1]

I have to replace some gears for a friend. They are for an arcade game which has a steering wheel and the gears are for control from steering wheel to position senser.

The smaller gear is   1.5″ ( 38.1 mm ) diameter with 24 tooth.

The larger gear is   3.27″ (83.05mm) diameter 54 tooth

I have no problem with cutting the gears as I have dividing head and a small mill etc but I don’t know what cutter to use i.e. what pressure angle etc to order a cutter for the job an so if anyone can help I would most appreciate it.

 

David

 

 

 

[JasonBModerator @jasonb]

Bit of an odd one there as I get 17.3333DP  or MOD1.465 or 0.181″ circular pitch

What are the gear ctrs as the OD may not be to the book and giving a false PCD

[DC31kParticipant @dc31k]

You would do well to discuss the practicalities of the top drawing with your client and give the CAD jockey a wrap on the knuckles.

A blind keyway is a challenge, so repeating it 24 times as a gear tooth up to a square shoulder will be a greater challenge.

Use two timing gears and a belt and hold the controller upside down.

As a very last resort, it may be possible to use 1.5 MOD gears and slot the holes in the position sensor to make the centre distance correct.

[SillyOldDufferModerator @sillyoldduffer]

I get the same odd-one answer as Jason, and guess it’s MOD1.5 with teeth clipped back slightly from 84.0mm to David’s 83.05 measurement.

Does anyone know of a simple way of identifying a physical gear’s Pressure Angle?  My book describes a fiddly process involving wires and a micrometer.  PA isn’t measured directly, it’s calculated from distance measurements.  And as the calculated difference between 14.5° and 20° is small, the answer isn’t crystal clear unless the micrometer and wires have  been manipulated skilfully.  Likely to be got wrong in my clumsy paws!  Never tried though.  Is measuring PA easier than I fear?

Dave

 

 

 

[Andrew CrowParticipant @andrewcrow91475]

Hi David, do the gears mesh with any others in the mechanism? If not you could use 18 dp or as suggested above 1.5 mod, pressure angle wouldn’t be an issue if they are stand alone.

Andy

[DC31k]

On DC31k Said:

You would do well to discuss the practicalities of the top drawing with your client and give the CAD jockey a wrap on the knuckles.

 

A blind keyway is a challenge, so repeating it 24 times as a gear tooth up to a square shoulder will be a greater challenge.

You would do well to look at the drawing again as I don’t see a blind keyway.

Though it  can be a bit tricky to model the gear profile as the cutter feathers out the teeth in CAD which may be what you mistook for a blind keyway

[Michael GilliganParticipant @michaelgilligan61133]

Not directly answering your question, Dave [S.O.D.]  … but will jump at any excuse to share this lovely animation

🙂

MichaelG.

.

http://www.homemetalshopclub.org/news/10/pressure_angle_anamation.gif

[John HinkleyParticipant @johnhinkley26699]

David,

How much, if any, leeway is there in the spacing between the gears?  Using my gear calculator. I get 84.00mm diameter for the 54 tooth gear and 39.00mm for the 24 tooth one :

 

John

 

[Michael GilliganParticipant @michaelgilligan61133]

Just a thought:

If the diameters were measured from the existing remnants [broken, and possibly Nylon66] they could be significantly out-of-spec.

MichaelG.

[David George 1Participant @davidgeorge1]

The original gears were moulded on to a brass core with flats and knurling to stop spinning on the core. The new ones are going to be cut from solid Delrin which will be ok strength wise. The edge of the thinner gear matches the side of the smaller gear so I can cut the tooth profile just slightly longer than the width of the gear and the rest can just be the radius of the cutter. The gears are mounted in 2 hole bolted bearing housings and there are about 3mm movement in sloted holes to adjust mesh of gears. It sounds like the original gear has some shrinkage and I will make my new gear 84mm diamiter to simplify maters 1.5 mod.

Thanks very much

David

[noel shelleyParticipant @noelshelley55608]

David, I would be tempted to look at DAVALL stock gears. They do a 24T 1.5mod and a 54T 1.5 mod, the small one in steel and the large one in polyacetal. Might be easier and quicker.

A previous post mentioned company catalogues, IF the above one is still in print it is VERY interesting, I believe it was mentioned in ME many (20 or 30) years ago, I got one ! Noel.

[Howard LewisParticipant @howardlewis46836]

Like the others, the dimensions suggest 1.5 Module gears, in which case the Pressure Angle is likely to be 20 degrees.

I think that Module Gear Cutters are numbered in the opposite sequence to DP cutters; so my guess is that for a 24T you will need a No 4 1.5 Module cutter, and for the 54T a No 6 1.5 Module cutter.

The depth of cut (D+f) will be engraved on the cutter

For the 54T you can run right through, but the 24T teeth will have a radiused end rather  than a perpendicular one, unless it is possible to reduce the OD of the blank end so that the cutter only just touches the reduced OD.

HTH

Howard

[OldironParticipant @oldiron]

Does it really matter what the DP or MOD is ?  It is an arcade game. As long as the tooth count is correct and the mesh is correct at the desired centres it will be fine. As suggested above by Andrew (Andy)  you could use 18dp.  You can always make dummies from wood to test the fit and adjust the diameters to suit.

[John HaineParticipant @johnhaine32865]

Given what David says about the function the torque transmitted will be minimal and pressure angle irrelevant.  Surely the most important aspect is the centre distance and any pair of gears of just about the right ratio would do the job.

[JasonB]

On JasonB Said:

Though it  can be a bit tricky to model the gear profile as the cutter feathers out the teeth in CAD which may be what you mistook for a blind keyway

No mistake.

The blind keyway is an _analogy_ to the teeth that stop at a square shoulder, which are impossible to cut.

—

With respect to determining pressure angle, a modern method could be to 3D print (or even perhaps inkjet print on transparent material) a sample few teeth of both possibilities and hold against the item.

[Stuart Smith 5Participant @stuartsmith5]

You could just buy the gears.

1.5 mod with the number of teeth shown are the same diameters as the drawing.

Bolton Engineering have hostaform ones. About £12.00 plus postage for the two.

Stuart

 

[Howard Lewis]

On Howard Lewis Said:

I think that Module Gear Cutters are numbered in the opposite sequence to DP cutters; so my guess is that for a 24T you will need a No 4 1.5 Module cutter, and for the 54T a No 6 1.5 Module cutter.

Module gear cutters are indeed numbered the opposite way round to DP cutters. The following module cutters would be needed: 24T – No.5, 54T – No.3. Although a moot point it might be better using a No.2 cutter for the 54 tooth gear as involute cutters are correct for lowest tooth count in the range but are slightly too curved for the higher tooth counts in the range. So a No.2 cutter, starting at 55T, might be a better match to 54T.

Julie

[Dave HalfordParticipant @davehalford22513]

The  plastic used in old coin-op’s either shrinks or swells with age so measuring the sizes today is not reliable. Your choice of 84mm is the right one.

[Dave SParticipant @daves59043]

If they are involute (which is likely) the the pressure angle is equivalent to the angle of the rack form tooth.

Very interesting you say, but how does that help?

Well rolling the gears along a thin strip of plasticine will produce such a rack, and then the angle can be measured directly.

Dave

 

[Pete RimmerParticipant @peterimmer30576]

If you;re making a pair of gears the pressure angle is irrelevant unless there is some engineering consideration for choosing one which there doesn’t seem to be in this case. Also, depending on the way it’s mounted I’d be very surprised if there wasn’t some adjustment in the centre distances. I’d make a pair of gears with either 18DP or 1.5MOD and make the results fit. Even if you had to manipulate the diameters quite heavily it would cause little problem for a simple position sensor.

[HuubParticipant @huub]

If you have a 3D printer, 3D print the gear to check the PA and module. The printed gear would probably be good enough to drive a steering sensor. PLA or PETG would be good enough for such a gear.

[Pete RimmerParticipant @peterimmer30576]

This application would be perfect for 3d printed gears.

[Phil PParticipant @philp]

Do you even need gears for this application ?

If all the gears are doing is driving a sensor, maybe a friction drive using an O-ring in a groove on the OD of one disc that could drive the other with maybe a knurled finish, all you need is the correct ratio and they can be made by simple turning operations.

The cost of two gear cutters will be quite significant, so it would be a cheap solution if it works out.

Phil P

[Dave HalfordParticipant @davehalford22513]

Arcade games are mistreated.

You can make a single point disc gear cutter as we are not matching other gears and only cutting plastic.

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