Custom Gearbox Without Automated Machining?

[Jared]

It's possible if you know what you're doing with the Bridgeport and pay attention to backlash.

To make the bearing bore, I'd probably use a boring head. If you don't have one and don't want to buy one, you can also buy a 1" drill bit ($10 for the cheapest reasonable one) and a 1.125" ream ($50).

I wouldn't use calipers and a punch. The center to center spacing of the gears needs to be within a few thousandths for the gears to not turn to dust in a short period of time.

[Cory]

Originally Posted by Jared

It's possible if you know what you're doing with the Bridgeport and pay attention to backlash.

To make the bearing bore, I'd probably use a boring head. If you don't have one and don't want to buy one, you can also buy a 1" drill bit ($10 for the cheapest reasonable one) and a 1.125" ream ($50)..

This is way too aggressive. You're not going to get good results with 1/16 stock removal per side.

Your pre drill should be 2-3% smaller than your finished hole. 1-1/16" in this case.

[asid61]

Just use the dials on the handwheels. Ordering a DRO is in your best interests, as they save a massive amount of time that is otherwise spent worying about backlash and tracking position. A "competent" machinist will not need a DRO, but it helps a ton for students who are learning. Add 0.002" or 0.003" between gear bearing holes to make sure that small tolerances don't kill the gearbox.
I usually just use a 1/2" drill, followed by a 3/4" endmill and then a 1" endmill to bring the hole larger, then finish with a 1.125" endmill. This makes a tight slip fit for 1.125" bearing OD, although not a press fit. You should always seek to retain bearings on a shaft with "positive" retention, which is things like shaft collars, screws, etc.

You will not usually need to make a custom gearbox. For drivetrain, I urge you to go COTS all the way to save time. For anything else, try using clamping gearboxes and bearing blocks from Vex, unless it's super heavy-duty. After exhausting those options, then, I would look into custom. Follow KISS principles in design when manually machining a gearbox.

[FrankJ]

Machinist were building gearboxes way before CNC and DRO although those are great tools if you have them. You can lay them out with a machinist scale and a scribe. Youtube is an incredible resource for this kind of stuff. Here a couple of videos comparing the different methods. I would recommend machining the side plates in pairs the whole match.

Hole layout part one

Hole layout part two

On youtube: mrpete222 has many great videos on old school machining. THATLAZYMACHINIST is another good source.

[asid61]

Originally Posted by FrankJ

Machinist were building gearboxes way before CNC and DRO although those are great tools if you have them. You can lay them out with a machinist scale and a scribe. Youtube is an incredible resource for this kind of stuff. Here a couple of videos comparing the different methods. I would recommend machining the side plates in pairs the whole match.

Hole layout part one

Hole layout part two

On youtube: mrpete222 has many great videos on old school machining. THATLAZYMACHINIST is another good source.

I love mrpete, but still strongly recommend against making FRC gearboxes with only prick-punch layouts. In the second video he compares the accuracy of three different methods (one of them being DRO) and he is still only getting around +/-0.005" on his holes- which is still better than the great majority of students will do. That kind of tolerance is unacceptable for even Vex gears. At the very least, use the mill's built-in dials to drill your critical holes like those for bearings.
This Old Tony is another good resource for machining.

[MikePerreman]

we went with calipers and punches, takes a wile, a few bumps along the way, but eventually we got it. Good Luck!

[AdamHeard]

Originally Posted by MikePerreman

we went with calipers and punches, takes a wile, a few bumps along the way, but eventually we got it. Good Luck!

Did you do this on a manual mill? or a drill press?

[ratdude747]

Originally Posted by FrankJ

Machinist were building gearboxes way before CNC and DRO although those are great tools if you have them. You can lay them out with a machinist scale and a scribe. Youtube is an incredible resource for this kind of stuff. Here a couple of videos comparing the different methods. I would recommend machining the side plates in pairs the whole match.

Hole layout part one

Hole layout part two

On youtube: mrpete222 has many great videos on old school machining. THATLAZYMACHINIST is another good source.

I'll add Keith Rucker as a good machinist on youtube:

https://www.youtube.com/user/ksruckerowwm

He's even milled gears for a blacksmith blower using a horizontal mill and dividing head. No DRO on that mill either.