Worm And Worm Gear For My Metal Bandsaw

Project:
Making a worm and a worm gear for my metal band saw

Difficulty Level (Easy, Medium, Hard, Insane):
Hard

Process:
There are a few tools I had to make first, before I was able to get started on the worm and worm gear, such as:

1. Fly Cutter
2. Dividing Head
3. 39 Tooth Gear
4. Internal Thread Cutter
5. Ejector Nut for Mill

Once all of these had been built, the first step was to create a change gear with 94 teeth to allow me to cut a thread with a .2618" lead. The math I used was as follows:

45 teeth (with the 8 TPI setting) = 0.125" lead
x teeth = 0.2618" lead

solving for x I get (45 * 0.2618)/0.125 = 94.248 teeth

If I round down to 94 teeth, the actual lead it would produce is as follows:

45 teeth (with the 8tpi setting) = 0.125" lead
94 teeth = x

solving for x I get (94*0.125)/45 = 0.2611"

Since a 94 tooth gear would produce a lead only 0.0007" off per thread and the worm has about 5 threads I would only be off by 3.5 thousands of an inch which in my scenario actually didn't matter at all because the  hob which creates the actual worm gear used the same lead.

The most accurate gear would have been a 106 tooth gear with a 9 TPI setting to produce a 0.2617" lead but because this was only a one-time deal I decided to stay with a gear as small as possible so as to not put too much stress on the lathe.

Now that I had all the math out of the way it was a fairly straight forward (but time consuming) process of

1. Cut the gear blank for the 94 tooth gear
2. Cut the actual gear
3. Mount the gear in the lathe
4. Cut a piece of 4140 steel to length, turn it and then cut the thread (worm)
5. Cut one half off and harden it
6. Take the other half and mill cutter slots out of it to make the hob
7. Harden the hob
8. Cut the brass gear blank
9. Use the dividing head to gash 20 slots in the gear blank
10. Use the hob to actually hob the gear

A few snags I ran into was that I did not use a metal core at the center of the 94 tooth delrin gear which caused it to actually slip and tear the crap out of the rolling pins I used to tie the two drive gears together. This in turn caused the ACME insert to bind up on the blank piece of metal which bent the snot out of it.

I ended up messing up TWICE until I decided I'd have to bore out the center of my 94 tooth gear and press fit a metal core into it. The third time I decided to take it very slow and instead of using a straight ACME insert I'd use a parting insert, cut a SQUARE profile into my worm and then use the ACME bit at the very end to cut the 29 degree angle which was required for my worm.

The tool holder I used was a Maxx-Edge ME2210210 NSR 12-3B and the insert I used was a NA3R4 KC850

That seemed to work out quite well. It still took me quite a while because it was (and is) still a learning experience for me. But once it was done I was quite proud and very pleased with the results.

After the worm gear was done, I had to cut a key way and drill/tap a set screw and I was ready to go install it in the metal band saw (blog to come).

Update:
Unfortunately, after a few hours of using the new worm and worm gear, the rough texture of the hardened worm wore right through the teeth of the worm gear leaving me with a stripped worm gear and some gear oil in the gear box that looked like it was a glitter paint art project.

I had suspected that this might happen and ended up having to take it all apart, put my worm and hob back on the lathe, and use my DIY Tool Post Grinder to grind them smooth.

After the worm and the hob were ground smooth, I re-cut a new brass worm gear and put it all back together. I checked it after about 30 minutes of running and although there is some brass dust in the oil, I think it's mostly from smoothing out the rough gear teeth. It certainly seems to be working a lot smoother. And, just in case I have to make another one in the future, I took really good measurements and drew it all up in AutoCAD. Hopefully, I won't have to ever make another worm gear for that metal band saw.

Videos:

 
Pictures:

The hodge-podge screwed-up fix of the previous owner

The broken worm

The broken worm gear

Another view of the 3 worm gear teeth that were sheared off

A paper sample of the required change gear

Raw stock of Delrin

Some calculations for cutting the 94 teeth

Cutting the gear blank out of delrin

The finished gear blank

Getting the dividing head set up

Using the 47 hole ring

Mounting the sector arms at 20 holes in the 47-hole ring

The crank handle installed on the dividing head

Using a diamond sharpening saw to create the profile for the fly-cutter

Close-up of the fly cutter tool

The shaped cutter installed in the fly cutter

Adjusting the height of the fly cutter to center height

Getting started on cutting the 94 tooth gear

Close up of the 94 tooth gear about half-way done

Cutting the last tooth

The finished gear before it was cleaned up

The finished gear

Cleaned and stamped with 94

The gear mounted in the lathe

The spec sheet for the worm and worm gear

Cutting off 6" of 4140 steel

Getting ready to turn the steel down to size

Turning the 4140 steel to size

Another view

This was the tool holder I used: Maxx-Edge ME2210201 NSR 12-3B

This was the insert I used: NA3R4 KC850

After the first scratch pass

Matching the old broken worm with the new steel blank

Almost done

The mangled delrin gear

After the center was bored out and a steel core was pressed in

The two gears that are linked together with two 1/8" steel roll pins

The two gears mounted together

The gear mounted in the lathe

Third attempt at cutting the worm

Close up after the square portion was cut out

The finished worm meshing nicely with the worm gear

Closer up after it was all cleaned up

Parting off the actual worm from the worm hob

The finished worm before heat treating

Another view

The heat treated worm

Another view

The new worm mounted on the metal band saw shaft

Milling the cutting slots into the worm gear hob

Another view

The finished worm gear hob

Turning a piece of 2.5" brass to size to make the worm bear blank

Closer up of the almost finished brass worm gear blank

The finished worm gear blank

Parting off some spacers for the mounting post that will hold the bear blank

Adjusting the gear blank to center height

Another view

Getting ready to hob the worm gear

A few minutes into hobbing the gear

Another view

The completely mangled up gear blank

Adjusting the angle of the dividing head to match with the angle of the worm gear

Another view

Making sure the dividing head is set at the right angle

Gashing the gear blank for 20 teeth

Close up of the beginning of the gashing process

Another view

The gashed gear blank

Another view

Getting ready to start the second attempt of hobbing the gear blank

Another view

The finished worm, worm gear, gear hob and the old worm and the old worm gear

Close up of the finished worm gear

Another view

Another view

Another view

Cutting the 3/16" keyway

The assembled worm gear

The dimensions of the final worm gear

Tools:
Metal lathe & accessories
Angle grinder
Measuring tape
Markers
Bench top grinder
Drill press
Cordless drill
Hammer
Propane torch
Bucket of water
Ear/Eye protection
Diamond grinder

Materials:
6" of 4140 (I actually used 18" because I wrecked the first two 6" pieces)
Roll pins
2" of 2.5" brass

Cost:
$25.00

Time:
20-30 hrs but much of it was learning and re-doing my screw-ups

Savings:
$200.00

Conclusion:
I am very pleased with how it turned out.