Gerald, you are confused with length of a shaft from the bearing to a gear wheel? In my case the shaft is made of stainless steel. For a usual steel there is more reliable configuration, but more bulky.

I am a little bit worried about the flexibility of the shaft. It is quite a long distance from the bearing to the pinion gear. There is no real difference in the flexibility of stainless steel compared to usual steel - the vibration frequency will be the same. It will be interesting to see if you get good cutting results.

Would something like a simple sintered bronze sleeve in the opening by the pinion gear help or hurt?

Gerald, I thought of it. For myself I have chosen a variant with stainless steel - there was at hand suitable preparation. And design more graceful. But the second variant obviously is stronger. And quality of processing we will see when will earn :)

It would remove the concern about flexing. But then that bronze sleeve becomes the most heavily loaded bearing in the system and needs to be upgraded for long life. Which puts you back to having a standard bearing there in the first place.

I think this picture at E-Z router is new. Might give some ideas; the shaft is static.

It seems to me, I have thought up an absolute variant of a reducer. It has a possibility to protect a belt and pulleys from a dust. In drawing I have designated a cover a blue line.

that is a good design - but for motors with different height it might be problem. so need to decide what depth it will be.
may be that can be left as a motor dependent variable.

also since the plate is laser cut on the pinion side a flange and bolt arrangement might not be necessary on the shaft case, we can just have the casing of the shaft match with the hole in the plate and make it go thru.

RGDS
Irfan

I like the way they did the stops.

But back to the belt drive plate, it would seem to my thinking that having the shaft that drives the pinon is less likely to have problems if it has two plates with bearings on each side of the larger toothed pulley.

I forgot the picture of the drive gear.

I was too quick with my comment about the link not work. Sorry!

I like the idea of a fixed shaft with only one motor plate.

The small pinion limits the shaft size though, i wonder if something like this would work?

...or you could weld the small pinion to the larger and just use the smaller diameter shaft.
That would make all your parts off the shelf and a simple "bolt" on like shaft for the assembly.

Just thinking outside the box.

We have a space constraint caused by our gantry and y-car end plates, which at present nearly touch the grub-screws in the pinions. (Due to the heap of guests in our house, I cannot access the cross-section drawing right now)

The interference issue seems to rule out fixing the pinion in the pulley.
how about this?
(pulley wheel is now narrower, for a 10mm belt)

Or maybe,

I think the overhang beyond the bearing is too much, and I don't really see the advantage in having a single plate.

I was mainly thinking of weight, but i suppose a single plate would have to be thicker, negating most of the difference.
The distance from the bearing was always a worry. initially it was much closer, but interference..well interfered :).

Hi:
What size and pitch is the rack gear?

the parts listed here are for the belt drives which has nothing to do with the rack and pinion, the rack is 20dp @ 20 teeth per inch same goes for the pinion,
and the pinions I run are 20 tooth..
//chopper

cncrouterparts belt drive
 

Take a look at cncrouterparts.com, they are selling a 3:1 belt drive, this belt drive is similar to the ez-router's belt drive. They show how the sytem works with two cool videos.

http://cncrouterparts.com/product_in...products_id=50

Edgar,

It looks like the 3:1 belt drive that you referenced is for use with 23-frame sized motors. I would not recommend that size motor. They're just too small for the job.

You´re right, the intention with my post is only to show the system because might give additional ideas.

Hello,

I have been a forum member for a while and just recently became extremely interested CNC routers. I have a degree in mechanical engineering and electronics and I am particularly interested in reduction transmissions for CNC machines. Over the last few months I have designed a belt reduction transmission that I would like to soon release! There are some great minds on this forum and it would be beneficial to receive some feedback before I finalize the design. I would primarily like to know the desired final gear ratio? The transmission will utilize either a nema 23 or a 34 motors. What would be a desirable final ratio for the design? The transmission can be between 3-1 and 9-1 with the current design. Any feedback would be appreciated.
Thank you,

Daniel Thompson

It is all a compromise . . .

3-1 is practical minimum for simplicity, low mass, low space needed, low cost, high reliability, high tolerance of flying dust, and still a significant improvement over a direct-drive.

9-1 sounds as if it will give the biggest improvement over a direct-drive, but how does it affect the other factors mentioned above?

The 3-1 is the most simple but the design is modular in that a second stage can be added at any time.
1. Mass
The transmission will be cast aluminum and will use aluminum pulleys for the reductions. The only parts on the transmission that are steel will be the shafts, bearings and some misc fasteners.
2. space needed
needed space depends on the final ratio so I don't have definite dimensions at this time. I certainly don't want to build a transmission that will not fit the mechmate requirements. Any information on size requirements would be appreciated!
3. Cost
Final cost will again depend on the ratio. Two stages will cost more than a single stage but will be worth the reduction. I can say that after I add the second stage cost difference between 3-1 to 9-1 is not significant. I will know more on cost after we do a prototype run with the casting shop.

4. Reliability
Reliability will not be affected by the final ratio. Pulleys and belts are selected to maintain a sufficient number of teeth in contact. I am working with Gates to select a belt size that will meet the tension requirements and still be an off the shelf item. Other factors such as shaft sizes and bearing placements are being considered and evaluated for deflections. There is a big difference in a part that works and one that works well:)

4. Dust

Currently the design is an open design , the belts and pulleys are exposed. We could integrate a cover into the design if needed? Those with open designed reductions how are the reductions tolerating the dust?

Thank you

The best ratio depends on the specific motor used. As you increase the reduction, you get diminishing returns, as the steppers torque drops as rpm's increase. Different motors have different torque curves, so you'd need to tailor the reduction to a specific motor/drive/power supply combo for maximum performance.

this maybe true but in the process of reducing the output it also multiplies the torque, so if you had a 450 oz-in motor and were using a 4 to 1 drive you would end up with 1800 oz-in of torque ( I am sure that a small amount will be lost in the transmission assembly) but for the sake of simplicity we will say it is zero loss so if you are running fast enough to loose half of your torque you would still be at 900 oz-in of torque which is well above what you would be getting from the oriental's with the 7.2's and I doubt that you would have that much loss or even close....
//chopper

Chopper, the oriental 7.2 behaves like a belt-drive at 7.2 ratio. For a discussion on the best ratio, there is no need to bring in a discussion of gear vs. belt.

. . . . and the type of cutting that you want to do, and the jog speed you want to achieve while not cutting.

On the cutting, working in soft woods is different to working in hardwoods.

The question of "which ratio is best" would be the same as asking the owner of a stickshift car "you can only have one gear - which one do you want?" (Of course, if you have a very powerful engine, the exact choice of gear is not so critical)