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SDL
02-24-2010, 11:22 AM
Does anyone know a good USA OR GB source of Circual Pitch gear cutters? Similar to the Mod or DP range.

Steve Larner

LES A W HARRIS
02-24-2010, 01:43 PM
Does anyone know a good USA OR GB source of Circual Pitch gear cutters? Similar to the Mod or DP range.

Steve Larner
Like these?

http://www.ashgear.com/fcp.pdf


Ash Gear,


cheers,

SDL
02-24-2010, 05:44 PM
Like these?

http://www.ashgear.com/fcp.pdf


Ash Gear,


cheers,


That's a good start, since found out that there is a special version of the std gear cutters for doing bevel gears, but we will contact them and see if they have the version.

Thanks

Steve Larner

macona
02-24-2010, 05:59 PM
Whats neat about ash is they will rent cutters as well, They also have an old stock area where things are much cheaper.

rohart
02-24-2010, 06:07 PM
Can you say where you found out about special cutters for bevel gears ?

Ivan Law says a reasonable approximation (for parallel depth bevels) is to cut the teeth as per the inner face and then to angle each way and take a strip off each side of the teeth. You don't use the cutter for the number of teeth, but the cutter for a larger number of teeth as he specifies.

I'd like to know what the options are for improving on this are.

SDL
02-25-2010, 03:33 AM
Can you say where you found out about special cutters for bevel gears ?

Ivan Law says a reasonable approximation (for parallel depth bevels) is to cut the teeth as per the inner face and then to angle each way and take a strip off each side of the teeth. You don't use the cutter for the number of teeth, but the cutter for a larger number of teeth as he specifies.

I'd like to know what the options are for improving on this are.

This is for a friends traction engine diff, I got involved as I did the maths according to the machinery handbook formulae, At one time he was going to use the nearest DP cutter to .3/8CP and got hold of some of the gear cutters same DP and cutter number but there was a differance in that the one engraved bevel gears was thinner at the tip. This made the gear too big so the hunt is on for CP bevel gear cutters. I will post more if we find them.

Mervs Burrel van be seen here http://www.banburymodelengineers.co.uk/trophy.html

Just needs the diff to run.

Steve Larner

Steve Larner

Timleech
02-25-2010, 03:45 AM
This is for a friends traction engine diff, I got involved as I did the maths according to the machinery handbook formulae, At one time he was going to use the nearest DP cutter to .3/8CP and got hold of some of the gear cutters same DP and cutter number but there was a differance in that the one engraved bevel gears was thinner at the tip. This made the gear too big so the hunt is on for CP bevel gear cutters. I will post more if we find them.

Mervs Burrel van be seen here http://www.banburymodelengineers.co.uk/trophy.html

Just needs the diff to run.

Steve Larner

Steve Larner

I've got a number of CP cutters, but I don't think any are for bevel gears. I'll check later.

Tim

oldtiffie
02-25-2010, 04:06 AM
I am a little intrigued about the use of "CP" gears as it suggests that they are for gears that mesh with a rack or a worm that has a linear fractional pitch instead of a pitch with a "pi" function as is the care with normal circular pitches which are derived from DP (inch = ((no. of teeth)/(pitch diameter))) or modular pitch (metric = ((pitch diameter)/(no. of teeth))).

I have read the item on it at page 2034 in my Machinery's Handbook 27.

Timleech
02-25-2010, 04:32 AM
3/8" CP is 3.03 module, so a 3 mod cutter ought to get you close enough if you can find one.

I'll post back later if I've got anything that might do.

Tim

Timleech
02-25-2010, 06:04 AM
Just checked, I've got a No6 cutter for 3/8 pitch bevel, 14.5 degrees. That's the only 3/8 bevel cutter I have, but I do have 1,2,4,6 & 8 straight cutters in 14.5 degree and 2,3,5,7,8 in 20 degree 3/8 pitch. Also 3,5,6,7,8 in 8dp bevel.

PM me if any of those would be of use.

Tim

SDL
02-27-2010, 06:09 AM
Tim thanks for the offer I will get back to you by PM if we decide we can use some the ideal is 0.375 CP Bevel cutters No's 3 & 8.

Does any one know if you just substitute the Bevel cutters for the standard ones.

Following a previous thread where I asked about calculators for bevel gears. http://bbs.homeshopmachinist.net/showthread.php?t=37291&highlight=Bevel+Gears
I did my own in Excel using the information in Machinery Handbook 27th Edition, the calculations are shown below and if any one is interested I will send them a copy if they PM me.

http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep1_0001.jpg
http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep2_0001.jpg
http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep3_0001.jpg

But I am now wondering what the effect of using the standard cutters is for bevels and if the Machinery Handbook is based on std cutters or bevel as I didn't know they existed until a couple of weeks ago.

Steve Larner

oldtiffie
02-27-2010, 07:36 AM
Steve.

Congratulations on a really good effort.

I will print it out and have a look at it tomorrow and will get back to you.

As you are using CP instead of DP cutters and as most calculations are based on DP (inch) or Module (metric) - I am guessing here - you may need to convert the CP>DP.

I have a copy of MHB 27 and will check that as well.

See MHB page 2091 (first paragraph) regarding the thinner cutters for bevel gears.

This link from Ringer:
http://users.beagle.com.au/lathefan/Cutting%20a%20bevel%20gear.pdf

at:
http://bbs.homeshopmachinist.net/showpost.php?p=480036&postcount=7

is a good summary of the method.

LES A W HARRIS
02-27-2010, 05:50 PM
Tim thanks for the offer I will get back to you by PM if we decide we can use some the ideal is 0.375 CP Bevel cutters No's 3 & 8.

Does any one know if you just substitute the Bevel cutters for the standard ones.

Following a previous thread where I asked about calculators for bevel gears. http://bbs.homeshopmachinist.net/showthread.php?t=37291&highlight=Bevel+Gears
I did my own in Excel using the information in Machinery Handbook 27th Edition, the calculations are shown below and if any one is interested I will send them a copy if they PM me.

http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep1_0001.jpg
http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep2_0001.jpg
http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep3_0001.jpg

But I am now wondering what the effect of using the standard cutters is for bevels and if the Machinery Handbook is based on std cutters or bevel as I didn't know they existed until a couple of weeks ago.

Steve Larner
N prime for your gear ratio of 12t pinion by 44t gear would result in bevel cutters #1 & 8, not # 3 & 8. MHB & OT's PDF link show that a milled bevel cutter is thinned down in order to pass through the toe end of the bevel pinion/gear. Then one has to rotate the gear & offset c/line by a calculated amount to achieve proper thickness.

Cheers,

Timleech
02-27-2010, 06:06 PM
N prime for your gear ratio of 12t pinion by 44t gear would result in bevel cutters #1 & 8, not # 3 & 8. MHB & OT's PDF link show that a milled bevel cutter is thinned down in order to pass through the toe end of the bevel pinion/gear. Then one has to rotate the gear & offset c/line by a calculated amount to achieve proper thickness.

Cheers,

As an 8DP cutter will be a whisker smaller than for 3/8" CP, what about using 8DP (if you can't find the right CP cutters) and just opening out the cut a fraction more to compensate? It's a fairly low speed application, I don't think the original traction engine gears were super-precision items.

Tim

John Stevenson
02-27-2010, 06:33 PM
As an 8DP cutter will be a whisker smaller than for 3/8" CP, what about using 8DP (if you can't find the right CP cutters) and just opening out the cut a fraction more to compensate? It's a fairly low speed application, I don't think the original traction engine gears were super-precision items.

Tim

Good call Tim, as an aside for the UK guys I called into Manor Foundry at Ilkeston last week and spoke to John the owner.
He's been advertising on the free adverts web site that they now do cast iron.

He showed me a sample which was a bevel gear for a traction engine, one of the side bevels as opposed to the pinions.
This was about 5" diameter, guessing 40 teeth about 10 DP.

The teeth were that smooth that they looked like a die casting, I have only seen castings like this on some of the very old Stuart engine kits.

I asked how much as an example and was told about 15.
All this gear needed was the bore boring out, no other machining or fettling was needed.

They do one off's or bulk and understand what people need, usual no connection other than the fact i have used this company for 15 or so years with no problems.

.

oldtiffie
02-27-2010, 10:28 PM
Originally Posted by LES A W HARRIS
N prime for your gear ratio of 12t pinion by 44t gear would result in bevel cutters #1 & 8, not # 3 & 8. MHB & OT's PDF link show that a milled bevel cutter is thinned down in order to pass through the toe end of the bevel pinion/gear. Then one has to rotate the gear & offset c/line by a calculated amount to achieve proper thickness.

Cheers,

Thanks Les.

I'd appreciate your help here in case I make a cock-up as well as any advice that you care to give.

I notice that in the first of Steve Larner's (the OP) pics of his table that he has a partial (8.33758) DP:
http://i757.photobucket.com/albums/xx218/steve_larner/Gears/Gears20375CP-sep1_0001.jpg
To be able to use a standard DP bevel gear cutter he will need to re-work his major PCD's (keeping the same 12:44 ratio) to use say 8DP.

Using CP (circular pitch) cutters is the hard way of doing it as MHB and just about everything else uses "full" or "half" numbered DP cutters (unless it is metric module). Metric Module is a PITA as MHB hardly refers to it at all and not at all in the relevant MHB tables.

Here is a conversion table for DP, CP and module pitches in which:
8 DP = 0.3927 CP=3.175 Module
3/8 CP = 8.377 6DP = 3.0319 Module
http://i200.photobucket.com/albums/aa294/oldtiffie/Black_book/BB_52.jpg

And here are the common (spur) gear formulae and relationships:
http://i200.photobucket.com/albums/aa294/oldtiffie/Black_book/BB_50-51.jpg

MHB 27 starts "Bevel Gearing" at page 2081 - and it is "heavy going".

Formulae and diagrams commence at page 2085.

Numbers of formed cutter table is at page 2089.

Offset for cutting bevel bear table is at page 2092.

The set-up for milling is at page 2093.

Measuring the tooth thickness with a gear micrometer:
http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Gear-measure1.jpg
can be a PITA - particularly at the "small end" as it relies on the OD of the work cone being very accurate.

It does not matter how it is "cut" but milling bevel gears is a "kludge" where a series of "work-arounds" is required.

In the long, long ago (50+ years!!) when I was cutting them, it was a PITA then too.

I certainly would NOT use the direction of cutting gas per Fig. 2 in MHB page 2093 as it is just asking for the cutter to crash into the dividing head. I have seen it happen (on the machine next to mine!!) and having a gear cutter climb milling up and trying to get over a dividing head is a sight and experience not easily forgotten.

Further, cutting in that direction (away from the dividing head) will soon find an end-play in the DH spindle as well as trying to push the job off the spigot/mandrel/arbor.

Reversing the direction of cut towards the DH solves those problems. It also ensures that the cutter gets the the job where the metal to be removed is thickest/deepest as well as ensuring that "rubbing" (before actually cutting) is minimised.

Filing the "small" end toward the "large" end is a PITA too as you are in effect simulating the "3-plate" method of getting three flat surface plates. It requires a lot of serious thought and patience as there is a lot of filing to be done in quite small increments if a good "fit/mesh" is to be achieved. It is very highly skilled work. It can be even harder that correctly "blueing-in" the mesh in the crown wheel, bevels and spider gears in an automotive differential.

Given the number of formulae involved, and the ease of making a cock-up in the use of them, I'd suggest that the OP expand his spread-sheet considerably. It may well be easier if a mistake is either made or is to be avoided.

But if it were me, I'd use full-number DP's and keep the required gear ratio.

John Stevenson
02-28-2010, 07:02 AM
I notice that in the first of Steve Larner's (the OP) pics of his table that he has a partial (8.33758) DP:

Using CP (circular pitch) cutters is the hard way of doing it as MHB and just about everything else uses "full" or "half" numbered DP cutters (unless it is metric module). Metric Module is a PITA as MHB hardly refers to it at all and not at all in the relevant MHB tables.



It's not hard it's just numbers.
He's not using a partial DP he's using CP and just as 25.4mm is equal to one inch it's a conversion into units that are better understood.

If you want to understand about gears then throw MHB away or better still use it to prop the shop door open and buy the series of Buckingham books and a few Jones thrown in for good measure.

These are the people who did all the work on gear forms and calculations, not the parasites at Machinery Press who scavenged everyone else's work to produce one of the most overrated books in history.

Circlip
02-28-2010, 07:12 AM
Oh dear, Sunday again. You've failed to mention John that you can only use the later versions of MHB to prop the door open, the spines crack on the early versions and the door just slides over the top.

Can't even design a good door stop.:D :D

Regards Ian.

SDL
02-28-2010, 08:27 AM
I

If you want to understand about gears then throw MHB away or better still use it to prop the shop door open and buy the series of Buckingham books and a few Jones thrown in for good measure.


What are the Buckingham books? can they be got secondhand.

I got into this as afavour to Merv to do the calculations as the drawings for the 3" Burrel dont give much info on the gears. He cut a test one of the big Bevel in Plastic using a std CP cutter but it didnt work out as the cutter was too wide at the narrow end. so we started looking for info on CP Bevel gear cutters but so far other than determiing they exist info is short.

He has cut all the other transmission gears and it runs fine on air.

This must mean the max lenght of the Bevel is govened by the cutter tip width as well, there a lot to learn here.

Steve larner

John Stevenson
02-28-2010, 08:57 AM
Steve,
There is a calculation that works out what standard cutter is the same as a bevel cutter.
I'll dig a book out later and post you the info.

I'll also email or Pm you some information on the Earl Buckingham books so the vultures don't descend.

SDL
02-28-2010, 09:04 AM
Steve,
There is a calculation that works out what standard cutter is the same as a bevel cutter.
I'll dig a book out later and post you the info.

I'll also email or Pm you some information on the Earl Buckingham books so the vultures don't descend.

Thanks that would be great.

Steve.

Timleech
02-28-2010, 11:38 AM
Steve,
There is a calculation that works out what standard cutter is the same as a bevel cutter.
I'll dig a book out later and post you the info.

.


John

Could you forward that info to me also please?

Thanks
Tim

LES A W HARRIS
02-28-2010, 12:16 PM
SDL,
Can you post a few more dims, the Mounting Distance is a major, your 12 X 44 Teeth can be laid out anywhere within the pitch cones calculated & the mounting surface. Allowing a standard DP/CP or MM cutters to be used.

Milled bevels have different root & face angles than generated ones, Know anyone with a #12 Gleason?

The bevel milling cutters have the same form as the spur cutters other than being thinned down to pass thru the toe end of the bevel gear. However the number of the cutter to use has to be selected based on the pitch angle, as I posted you need #1 & # 8 for 12 x 44 ratio.

Cheers,

SDL
02-28-2010, 05:41 PM
SDL,
Can you post a few more dims, the Mounting Distance is a major, your 12 X 44 Teeth can be laid out anywhere within the pitch cones calculated & the mounting surface. Allowing a standard DP/CP or MM cutters to be used.

Milled bevels have different root & face angles than generated ones, Know anyone with a #12 Gleason?

The bevel milling cutters have the same form as the spur cutters other than being thinned down to pass thru the toe end of the bevel gear. However the number of the cutter to use has to be selected based on the pitch angle, as I posted you need #1 & # 8 for 12 x 44 ratio.

Cheers,


Thanks for the Info, on the cutter numbers, just had another look in machinery handbook and the Info is there but spent so much time getting the maths to work missed the fact that it was different to the std gear cutters, thanks for the heads up.

Although a Gleason would do a better job Merv has made all the other gears, and fabricated a lot of the bits that look like castings so I think the wish is to make it all now.

I am seeing him Wednesday and will try and get the extent of space available as a drawing. I did try calculating it as 8DP but it made the OD of the Big gear bigger than the metal blank.

Steve Larner