Gear cutting

[str8axle57Participant @str8axle57]

Hi everyone,

my name is Bill and I’m 64 years young. I’ve been a machinist for 51 years and at the end of the year I want to retire. I help out at a local hobby store working on old tinplate trains and the owner of the store asked if I could do some gear cutting to make for trains and I agreed. So now I have a Barber Colman 6-10 machine but I’m having trouble with the speeds and feeds. I was hoping someone could help me out with this? It’s been over 30 years since I did any gear cutting. Thank you

[DiogenesParticipant @diogenes]

The Barber Coleman 6-10 is a horizontal hobber; gleaned from the ‘net;

Machine Specifications are as follows:
MAXIMUM WORK DIAMETER:…………………………………………….6″
MAXIMUM TRAVEL OF HOB CARRIAGE:………………………………..10-1/2″
MAXIMUM DIST. SPINDLE FACE TO TAILSTOCK CENTER:………………….15-3/4″
MAXIMUM DIAMETRAL PITCH, 1 CUT:…………………….16 DP – 2″ DIAMETER
MAXIMUM DIAMETRAL PITCH,1 CUT:……………………..48 DP – 6″ DIAMETER
MAXIMUM HOB DIAMETER:…………………………………………2-1/16″
HOB SPEED:…………………………………………….133 – 533 RPM
WORK SPINDLE BORE:……………………………………………1-1/32″
WEIGHT OF MACHINE:…………………………………………3,500 LBS.

 

So is it correct that will these be smallish fine-pitch gears & pinions in ?brass?

 

 

[JasonBModerator @jasonb]

To a large extent speed is determined by the material being cut and the diameter & material of the cutter. Feed is related to the above and the number of teeth.

Letting the forum know these factors will help

[str8axle57Participant @str8axle57]

Hi gents,

thank you for your answers and yes they will mostly be made from brass. Some will be 1018. The gears we’re replacing were phenolic and had steel gears pressed into them. Most of the gears are 1 inch and smaller. There are larger gears for the standard gauge trains for their drivers.

[bernard towersParticipant @bernardtowers37738]

That sounds lie quite a machine for your size gears, pity you didn’t find a little Mikron machine I use mine to make down to 7mm dia. Best of luck.

[Michael GilliganParticipant @michaelgilligan61133]

By way of consolation … I know that Mercer used a very substantial machine to make the wheels for their Dial Indicators … I saw it running, back in the day.

I don’t have any photos of my own, but will have a browse later

MichaelG.

[Thor 🇳🇴Participant @thor]

Hi Bill,

There are online calculators, like this one: https://littlemachineshop.com/Reference/CuttingSpeeds.php#Milling

 

Thor

[DC31kParticipant @dc31k]

Would it be correct to say the gears are relatively thin? Some of your difficulties could be the stock flexing.

In a production environment, those gears may have been cut as a stack of a dozen or more. Hence, if now cutting individually, a backup flange just a little smaller than the root diameter of the gear could help stiffen things up.

[str8axle57Participant @str8axle57]

Hi guys,

Bernard, yes it is a great machine for what I need to get done and thank you

Michael, that must have been something to watch working.

Thor, thank you so much. I will check that site out.

dc31k, yes a lot of the gears are about 1/16 thick and some are 9/32” thick. Yes I do about 20 at a time. The machine has a 10 1/2” table. I also have 2 table top machines in my basement.

[DC31kParticipant @dc31k]

Just in case you did not find it, there is some useful information at vintagemachinery.org:

http://vintagemachinery.org/mfgindex/detail.aspx?id=5008&tab=3

You need to find or reproduce the slide rule shown here:

https://www.worthpoint.com/worthopedia/barber-colman-company-hand-book-490891360

This book is also worth looking for from time-to-time:

https://www.abebooks.com/first-edition/Barber-Colman-Handbook-HOBS-Precision-Tools-Company/32088626588/bd

Edit:

The handbook at vintagemachinery is captioned for a 6-12 but if you download it is actually for a 6-10, which the OP has.

[str8axle57]

On 28 May 2025 at 22:11 str8axle57 Said:

Hi everyone,

my name is Bill and I’m 64 years young. I’ve been a machinist for 51 years and at the end of the year I want to retire. I help out at a local hobby store working on old tinplate trains and the owner of the store asked if I could do some gear cutting to make for trains and I agreed. So now I have a Barber Colman 6-10 machine but I’m having trouble with the speeds and feeds. I was hoping someone could help me out with this? It’s been over 30 years since I did any gear cutting. Thank you

Hi Bill,

If you have the Barber Coleman do you have all of the change gears for it and do you also have the hobs that you need?

As for feeds and speeds the feed is determined by the tooth count, for higher tooth counts you use a higher speed ratio on the feed gears. This is because the feed rate is per revolution of the workpiece so if you use the same feed rate for a 20 tooth gear as a 100 tooth gear the chip load for the 20 tooth gear will be 5 times greater.

For speeds in brass go flat out, in free-cutting steel with a 2″ hob I’d say 200rpm is a safe bet for a HSS hob.

[str8axle57Participant @str8axle57]

Hi Pete,

Yes I have all the gears and hobs. The gears were in a 18” by 28” crate and the hobs were in a 12”by 12”by 12” box. The machine was in Illinois and the gentleman who was using it was 94 years young

[Pete RimmerParticipant @peterimmer30576]

OK then.

Assuming that you’re only cutting spur gears you’ll need the Barber Coleman handbook/operating manual for that machine which will give you the change gear setup and if your machine is capable of helical gears you’ll need to disengage the differential and lock it so that it doesn’t try to cut a bevel.

LINK to manual

You have the following considerations:

Hob speed in RPM. The book will advise but I’d go for around 200RPM as a baseline for a 2″ hob.

Tooth count. You’ll need to arrange the indexing gears for the required tooth count according to the operating manual pages 34-37

Feed rate. The manual will again suggest to you an appropriate feed rate on page 25. As I said in my post above the lower the tooth count the faster it will traverse giving you a heavier cut. If you use too fast a feed you’ll overload the machine and if you go too fine you may blunt the hob (or fall asleep)

Hob hand and helix angle. Most hobs will be right hand but you must check. You can read the helix angle off the hob and rotate the hob swivel to the angle given. i always check that I have set the correct angle by putting the edge of a steel rule into the helix on the SAME SIDE as the workpiece, and for a spur gear the ruler will rest parallel to the work shaft.

You MUST use cutting oil on steel if you want your hob to last

Inspect the cutting edges around the hob with a loupe or magnifying glass. If they appear even slightly blunted don’t use that hob until it’s sharpened. When they go blunt they can very quckly be destroyed or at least require heavy grinding to get back to a good cutting edge if you continue to use them, just like involute cutters.

[str8axle57Participant @str8axle57]

Hi Pete,

Yes I do have the operators manual. It’s the tan and brown book, it covers 6-10 through 16-56. What I was hoping for was someone who may have ran one and knows the correct speed and feed gears to accomplish the gears I need to make. If this makes any sense.

[Pete RimmerParticipant @peterimmer30576]

If you want hand-on experience go to practicalmachinist.com there are several time-served gear machinists there. Otherwise it’s all in that book. There’s a lot of formulae in the book that you can disregard for the gears you’re cutting and trying to read all of it could be overwhelming. If you want to know how to set up for a specific gear DP, tooth count  and material post it here and I’ll try my best.

[str8axle57Participant @str8axle57]

Pete,

yes overwhelming is the perfect word and I understand it wants to cover everything for the average operator. 😂🤣

[Pete RimmerParticipant @peterimmer30576]

If you’re cutting only spur gears you need Table 11 to set the index gears for the tooth count of the gear you are producing. Your machine turns the hob spindle at a 12:1 ratio to the work spindle so if you set up those gears as 1:1 ratio you’d be cutting 12 teeth (in fact the 12 tooth setup in the table is 90/45×36/72 =1).

So select your index gears for the required tooth count and assemble them on the machine according to fig. 1.

Next you need to set the RPM of the hob and feed rate which are both in Table 13. A 22/32 gear set on the speed gears will give you 183rpm for the hob see fig. 3 with the smaller gear lowest.

For a 30 thou per revolution (of the work) you’d set the feed gears in fig. 2 to 24 – idler – 60 with 24 on the left and 60 highest.

These are your three basic change gear settings you need for cutting spur gears. You don’t have to worry about the complicated formulae involving C constants or anything like that which is further down the manual, those are for cutting helical gears.

If you set your machine with those settings, read the helix angle and depth of cut d&f off the hob you’re using and set the hob slide swivel to the correct helix angle you could make yourself a gear blank and take a very light cut on the OD. I will be very obvious if you have got your setup wrong and if you only cut a couple of thou deep no harm will be done. Plastic or aluminium are good choices to make practice gears.

[str8axle57Participant @str8axle57]

Pete,

Thank you very much this is very helpful. I did find the pages you referenced me to. I’m going to go over to work and try this out. I do have a piece of brass on the machine that I can use. The gear I need to make is 44 teeth and it gets another gear pressed onto it and that is 16 teeth. It’s 3/8” OD.

[Pete RimmerParticipant @peterimmer30576]

16 teeth 0.375″ OD is a 48DP gear.

[str8axle57Participant @str8axle57]

Good morning Pete,

And thank you, I tried that yesterday afternoon and just took a scratch cut and it worked. So I have the gears figured out for one set of gears now I have to figure out for the other ones I’m going to need to make. I appreciate your help.

[Pete RimmerParticipant @peterimmer30576]

Glad its working out for you.

One good trick I use when setting up for hobbing is put a pen mark on the work and run the machine with the hob close but not touching. You can watch the work rotate and see if the pen mark travels round in time with the hob spiral. It’s a good indicator that you’ve got the index gears set up right.

[str8axle57Participant @str8axle57]

Hi Pete,

Yes that’s an old trick that I’ve always used. It’s good for keeping you out of trouble or getting into trouble.

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