Belt Driven Transmission

[richards]

Since the other thread discussing the 3:1 belt-driven transmission has become so long, I thought I'd show the aluminum version in a new thread.


7804


7805


7806

This version was cut out of 1/2-inch thick 6061 aluminum on my Alpha at 12,000 RPM, 0.60-ips XY-axes, 0.05-ips Z-axis, and 0.075 inch stepdown per pass using a HSS 3/8-inch cutter designed especially for aluminum. To run at those terrific speeds (ha!), I had to flood the cutter with tapping fluid designed especially for aluminum. You can image the mess that made!

This version is basically the same as the polycarbonate version except for some minor sizing changes and the use of shoulder bolts (thanks Harold Weber for the suggestion).

The 3:1 ratio works very well for the kind of work that I do. If you look closely, you might see the total absence of 'chatter' marks on the aluminum. I didn't do a full pass finish cut, so you'll notice some edge marks that would have been eliminated if I had used real flood cooling and then finished things up with a full depth finish pass.

[joe]

Nice work Richard, Keep it up.

Joe

[pfulghum]

Mike,
How big are those spacers?
How long is the lower shaft?

The motor mounts into slots to control the belt tension right?

Will 1/2" Delrin be ok?

-- pat

[richards]

Pat,
The four spacers (one is not shown in the photos) are 1.5" long x 1" diameter. The motor size diagram from Oriental Motor for the AS911AA motor was used to get data for the motor pockets. When the data was transfered into AutoCAD LT, I elongated the protrusion about 5/8", with 1/2" to the upper side and 1/8" to the lower side. The bolt holes in the mounting plate were converted to slots, again 1/2" longer on the upper side and 1/8" longer on the lower side. Finally, the pocket for the motor was widened about 0.1" on each side to give the motor clearance and elongated 1/2" on the upper side and 1/8" on the lower side. With the enlongated pockets the motor can move enough to tighten the belt.

Delrin will work perfectly. I've used Delrin, polycarbonate, and aluminum. All 1/2" thick. All worked perfectly. The motor does run just a little bit hotter, because it's turning 3X faster, so I decided to try aluminum so that it can also act as a heat sink. However, the motors have never gotten hot, just warm to the touch, so plastic should not be a problem. (With only a few weeks of actual running, I can't say for sure about the plastic, but after running during the hottest weather of the summer, everything has worked great with plastic - and it sure is lighter in weight than the aluminum.)

[richards]

Pat,
I missed the question about the shaft length. It's 5" long. Longer won't hurt, but anything shorter than 4-1/2" is going to cause problems.

[pfulghum]

Here is my order to mcmaster.com....

QTY 3
6495K732
Trapezoidal Tooth Timing Belt Pulley XL-Series, Fit 1/4" & 3/8" W Belt, 3.8" Od, 60 Teeth
$29.10 Each $87.30

QTY 6
6462K16
Type 303 Ss Set Screw Shaft Collar 1/2" Bore, 1" Outside Diameter, 7/16" Width
$3.40 Each $20.40

QTY 6
6384K49
Steel Ball Bearing Plain Double Sealed for 1/2" Shaft Dia, 1-1/8" Od
$6.90 Each $41.40

QTY 3
6495K718
Trapezoidal Tooth Timing Belt Pulley XL-Series, Fit 1/4"& 3/8" W Belt, 1.502" Od, 20 Teeth
$14.28 Each $42.84

QTY 4 (1 extra)
6484K225
Trapezoidal Tooth Neoprene Rubber Timing Belt .200" Pitch, Trade Sz 150XL, 15" Outer Circle, 3/8" W
$4.00 Each $16.00

QTY 3
5172T13
Steel 20 Deg Pressure Angle Spur Gear 20 Pitch, 25 Teeth, 1.25" Pitch Dia, 1/2" Bore
$13.55 Each $40.65

QTY 3
6061K428
Hardened Precision Steel Shaft 1/2" Od, 5" Length
$4.37 Each $13.11


QTY 14 (2 extra)
92230A330
Zinc-Plated Stl Female Threaded Hex Standoff 1/2" Hex, 1-1/2" Length, 1/4"-20 Screw Size (Same as 92230A007)
$2.77 Each $38.78

1 Pack
91355A083
Flange Button Head Socket Cap Screw Alloy Steel, 1/4"-20 Thread, 1" Length, Packs of 25
$9.03 Pack $9.03

Merchandise Total $309.51


Delrin (local supplier) - $60

Fun in the shop - Priceless


I did go with the 25 tooth spur gear for smoothness. This will give me a ratio of

60/20 (Transmission) * 20/25 (Spur Gear) = 2.4x over a stock alpha.

-- pat

[richards]

Pat,
Almost everything looks pretty good to me. I'm a little concerned about the standoffs, but have no real basis for the the concern. I used something similar from Home Depot on version 1. The assembly had a little too much flex, but I can't say that it was the standoffs that caused it. In any case, the standoffs could easily be replaced with something else, if flex is a problem.

You've done a little better than I did with prices. I figure that parts per motor are about $160 - $175, depending on shipping. When you figure in labor at $60 an hour, the price escalates to $370 per motor. Add in a 15% profit margin, and the price comes to $460.50 per motor. That is pricey, but considering the cost of 'chatter', it's still a bargin to me. (Don't forget to multiply that by five for the five versions that I've gone throught before being fully satisfied that I've done the job properly, and you'll end up with a big dent in your wallet. But as they always say, if a job is worth doing, it's worth doing well.)

[Brady Watson]

Nice work Mike. It's always nice to see 1st class work & ideas that come into fruition.

-B