Home made Gear Hob

[Jyman]

Hey guys,

So I made a gear hob last night, as you can see in the picture it's on the right. And yes it only has three cutting teeth as to the usual 5. So I know my gears will not be perfect. My question is would you harden it or would you just try it as is? It's only cutting a brass and an aluminum gear.

View attachment ImageUploadedByModel Engines1483462877.129388.jpg

 

[Brian Rupnow]

Harden it.

 

[BaronJ]

Harden it.

I agree, but don't make it glass hard.

 

[Jyman]

Ok, so harden it but temper it back down some. Any recommendations as to what temp to temper it to?

 

[Brian Rupnow]

It depends on what material you made it from. If you used oil hardening or water hardening steel, heat it to a bright orange with oxy acetylene and quench it in oil or water. Then put it in the oven for an hour at 300 degrees to draw it back. If it is a case hardening steel, then I can't advise you.

 

[Jyman]

Ok thanks, i think it's W1 steel that I used, so I will stick it in my forge tonight and then throw it in a bucket of water. And hope for the best that it is W1. Someone(my dad) likes to dig thru my metal bins when they need a piece, which in turns mixs everything up.

 

[Jyman]

Ok I hardened it and set up a piece of aluminum, and started cutting

View attachment ImageUploadedByModel Engines1483504323.597338.jpg

Going around

View attachment ImageUploadedByModel Engines1483504348.946145.jpg

And here is nervous part, when you get all around and see if it works.

View attachment ImageUploadedByModel Engines1483504416.730176.jpg

Woohoo it worked, but I did notice that the cutter is off on the line up or the cutter it's self is not made just right. So I will try again but for right now it might work alright.

View attachment ImageUploadedByModel Engines1483504500.065152.jpg

 

[Jyman]

This gear hob cuts so much faster then a single point cutter. it was about 30 mins to cut the gear and part it off, where as when I used a single point it was closer to 2 hours. And with the hob it was a smooth and quieter cut

 

[BaronJ]

That doesn't look too bad for a first attempt at a hob.

Now you need to cut another one and see how the two fit together, that will tell you if you got it right.

 

[Wizard69]

Ok thanks, i think it's W1 steel that I used, so I will stick it in my forge tonight and then throw it in a bucket of water. And hope for the best that it is W1. Someone(my dad) likes to dig thru my metal bins when they need a piece, which in turns mixs everything up.

Oven tempering should be fine. A quick search on the net should get you some charts for precise numbers but 400°F for greater than a hour should work out well. It really cones down to the alloy and how far back you want to draw the part down. That will vary a bit with application.

 

[Blogwitch]

Rather than messing about with ovens and such, do it like most people do, with a blowtorch, it only takes seconds.

Watch this Clickspring video, if you can't watch it all (well worth it) then go to 4 minutes and he shows roughly how to temper using a blowtorch. Just point the torch at your hub and when the straw colour gets near the tips move the torch away and quench the part.

[ame]https://www.youtube.com/watch?v=nZsnGhwsjjo[/ame]

If you go to the next video by clicking on the link shown at the end of the above video, it shows how he made a special cutter and how he heat treated it.


Hope this helps

John

 

[Jyman]

Thanks for the video about hardening. Well I cut another gear and realized two things.

1. The hob has one section that's a little wide on the cutter never noticed that before. Will probably make a new hob because of that.

2. The first gear I cut wasn't deep enough, I must have made a mistake when I measured. Next time I will have to measure better.

Anyone else see anything about them

View attachment ImageUploadedByModel Engines1483755234.001488.jpg

 

[John S]

Looks like you lost the tip of the cutter on one side. It's forming a step in the root.

Just off out now but will posts some views on hardening when i get back and this is from past experiences.

 

[John S]

In a previous life I had to make cutters for cutting wooden parts in the piano industry, now don't just yawn and go back to sleep. Believe it or not these were precision parts. The maximum tolerance we were allowed on any part was plus or minus two thou and this was the blank cutoff.
Holes had to be bored to 1/2 a thou, all day, day in day out on tens of thousands of components.

Most of our cutters were shaped form tools not unlike involute cutters, with special shapes, serrations etc.

Most of the special ones were made from 2" blanks of oil hardening steel as this was all we could manage to work on site.

Previous attempts of having these cutters made out had turned out to be unsatisfactory in term of shape and tolerance and also very, very expensive.

So we blanked a soft cutter out , gashed it and finished it using a full sized 1" bore Eureka attachment. Then it came to hardening.
These were sent away to be professionally hardened and tempered at a local company who did a wonderful job, they came back with a completely even straw colour. We then ground the face gash up to get a sharp cutting edge and they went into service.

Although they started off cutting well even on wood which when you are using exotic species can be abrasive they never kept the edge and gradually got worse.

We eventually put this down to the fact that the grinding whilst being done dry like most T&C grinding operations was reducing the temper which isn't high to start with. So the next cutters were hardened only and the heat put into the cutter from grinding was the tempering operation.
These were quenched immediately from grinding and fitted to the machines.
This increased the life between regrinds considerably.

Now brass and alloy is not far removed from wood it terms of machinability so the same method will work on these materials and will increase cutter life.

 

[Jyman]

John s,

Thank you it might be something for me to try on the next one, which will be made probably in the next couple days.

 

[mc_n_g]

I did mine on a lathe and cut it like a rack of gears.
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/DSCN9757_zpsca606afd.jpg

The only form you need to worry about is the single cutter you plunge in which has straight sides.
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/Making_hob_zpsd2c3dcbf.jpg
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/Cutting_flutes2_zps43446c03.jpg
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/All_flutes_cut_zps16ff59f3.jpg
Left about 0.005" on the tooth side so I could grind the teeth to make them sharp after hardening and tempering.
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/Cutting_18DP_teeth_zps8d836b29.jpg
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/cut_gears_view2_zps9c1024fe.jpg
http://i10.photobucket.com/albums/a140/mc_n_g/machinery/gear_zoom_facets_zps585ffafa.jpg

There are several sites you can use for proper depth and tooth form. I made my cutter for 18DP.

Another excellent site for single cutter making with great images is http://www.deansphotographica.com/machining/projects/multipoint/multipoint.html
Not my site but a great method and it is indexable for sharpening. Very well thought out.

 

[Gordon]

For the last year or so I have been making special cutters like counterbores, valve seat cutters and other special cutters and it is much easier than you would think. I make then from water hard drill rod, heat them to carrot color with the acetylene torch and then put them in a toaster oven I bought for $15 from Goodwill. Well worth the effort even if you are only going to use them once. I am starting to get a small collection of special made cutters. I also have had good luck making gear cutters. Even made a special worm gear for a small rotary table I made. That worked well because I could make a special pitch like 1/10 to get an even decimal rotation on the table.

 

[Jyman]

Mc_n_g I made mine the same way except I made mine out of 4140, I have some 1inch W1 but I don't have a lot of it, the steel store sold me it as scrap for $4.5 a pound. If it wasn't sold as scrap then I probably wouldn't have any because the tool steel is really expensive around town here. I bought some 3/8 tool and it was $1.5 an inch and would hate to see what some 1 inch would cost. I also made it so I could put it on a arbor, that way I could take up less room in my tool box for storage. As well as use less tool steel when i get the nerve to use my W1.

When I looked at my last cutter I noticed one of the side tooth formers was about 1.5 wider then the others which I think could have caused the notch in the tooth form. I was in a little bit of a rush when I made it as i don't get a lot of shop time (work way to much) and I really wanted to see if it would work like everyone else has shown online. So ether I will try and remount it on the lathe and fix it or I will scrap it and make a new one that size. Haven't decided yet.

 

[BaronJ]

Hi Jyman,

If you have hardened it, you might find that you have to grind the cutter to fix the bad profile !

I would start again and take a little more care in getting the profile right. As far as tool steel is concerned, have a wonder around your local scrap yard, old drills are worth picking up. The shank is relatively soft and hardens well. I've salvaged a couple of broken drills that way.