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)

Gerald,
there was no intension of discussing belt drives vs. the 7.2's
the only reason was for the loss that is generated through the gear drive which limits the 7.2's to around 700 to 750 ozin and all I am saying is if the 7.2's will drive the gantry with 700-750 ozin then the other reduction will be fine with a 50% loss of power since it will still have more than the 7.2's
and the reason I compared to the 7.2's is it seems to be the standard that is used here
//chopper

There is a serious misunderstanding of the amount of torque available from a "OM 7.2" motor/gearbox package. It gives a lot more than 700-750 ozin, but the spec says that you must not design your system to use that extra torque. Same goes for the belt-drive - the thin belts that most use for these reductions should also not be used at the torques levels that are needed on our routers.

For the OM 7.2, there is NO "loss that is generated through the gear drive which limits the 7.2's to around 700 to 750 ozin" That limitation is put on by the design engineer who needs to guarantee you long life running 24/7 under full torque.

Gerald,
if the engineers limit the torque it is for a reason, that being it will cause gear wear or failure, in other words the gear box cannot handle the load, so what good is a higher rating of torque if you cannot use it?
so the limitation of the 7.2's is going to be at the rated torque which is in the 700-750 oz-in range which quite frankly I could care less about.
but as far as the belt drives go the xl belts with .375 inch width have a breaking point of 390 lbs, which is equal to 74,880 oz-in
so if the operating range is say half of the breaking strength that would put us at 195 lbs or 37,440 oz-in which is way more than these motors can produce, I also have to believe that the operating strength of these belts would be closer to 75% of the breaking point which would be 292.5 lbs.
or 56,160 oz-in which is also way more than the motors will produce.
so I guess I will have to disagree with you that these smaller belts will not handle the load, the specs show that they will, and can handle the load what you have stated is incorrect.
//chopper

Chopper, for belt drives, the engineers publish charts like this:


The bottom left corner of the chart starts at 0.1kw (100 Watts) and 100rpm., which would be quite a common situation for us with our routers. The engineers there deem it too much for a XL belt.

This is just a general example of what the supplier's (belt or gear) engineers put out in public. But we have seen that our router application happily runs beyond the supplier's spec . . . . . for both belts and gears.

A chart which says to limit XL to 180 oz.in torque:
http://www.torquetrans.com/pulleys/t...lt-pulleys.pdf

http://www.misumiusa.com/CategoryIma..._pdf/p2823.pdf

http://www.roymech.co.uk/Useful_Tabl...ing_belts.html

http://mechatronica.eu/en/design-man...%20(21-26).pdf

Gerald,
I have never found charts like that before,
but I also didn't see the charts list what belts they were testing,
and what I mean by that is what type of material the belt was made from and what type of material was used to reinforce the belt, unless I missed it....( the belts I am running are reinforced with Kevlar and are much stronger than the regular XL belt)
there is a lot of reading there and I am not going to go through everything,
what it comes down to is you may want to run a heavier belt so built a transmission with a heavier belt, not a big deal, I have had zero problems with the XL's I am planning on changing them out every so often which I feel would be good maintenance. I don't know if this is necessary I will monitor them, to see what happens, also the pinion will walk out of the rack before you could put enough force on the belts to damage them.
but the issue still remains with the back lash in the gear heads of the OM 7.2's
and this you cannot get away from with out switching out the transmissions,
I am only stating what I have done you can choose to use the information or not, it really doesn't matter to me my machine works and works well, with great cut quality that quite frankly I thought I would never get from this type of machine, I also know that it is not a fluke since I have had the same result on two different machines, the second machine had a bad chatter issue just as bad a Nils, if not worse, in fact it was so bad that when he cut a file and the machine would come back to zero it would not be in the same spot, which was caused by backlash, once the belt drives were installed the problem was gone, you can run a file over and over with 100% repeatability
and accuracy, on both our machines,( just the other day I ran a repeated file over and over the first few cut parts were not deep enough so I adjusted the depth and cut the rest of the pieces and set the first part back in the jig and it dropped right into the drilled holes with out even touching the sides of the existing hole) I know you cannot do this with the 7.2's,(I had them on my machine ) now maybe you don't want to or need to have that kind of accuracy,and again I really do not care but I thought why not make the machine as accurate as possible,
that is why I shared what I had done, I am not trying to mislead anyone
all I have to say is the proof is in the cuts,
also I want to ask if any one using there mechmate can get this quality of cut with there machine, I really want to know I mean no disrespect this is a request to see the cut quality comparisons if you need to know it was cut in 6061 .250 thick on the diagonal to the machine, ( with a Milwaukee router) I am quite sure that you will not see the 7.2's be able to accomplish this, again this is from my experiences, with having the 7.2's they seem to be tight at first but as they break in the backlash becomes apparent..I am not going to argue about belt vs 7.2's this will be my last statement on the subject unless asked, you can see that they work by the quality of cut produced,
//chopper

Relax a bit Chopper. Nobody is saying that you have built a bad drive, and nobody is saying that the backlash in a geared motor can be ignored.

I do not understand how these marks. . . .


. . . . can be caused by backlash in a geared motor. Those marks are about 1/4" apart. (since been confirmed that material is 1/4" thick)

Did you see such widely spaced, very regular marks when you were running geared motors? I cannot recall that your "before" photographs showed anything like this.

Bear in mind that there are many other users out there with geared motors who are not seeing these wide apart, even spaced marks. (I don't call that "chatter")

Gerald,
mine were similar but not as deep,
the other machine that my friend has was very similar to this if not worse..
what I think happens is once the first pass happens it sets the chatter for the rest of the passes, the bit will follow the path of least resistance and that is why you end up with the chatter lining up from top to bottom, on different cut paths, I also believe that the equal marks along the cut path are generated by the tool, because it is say a two fluted up spiral bit it will grab or dig into the material at equal measurements, since the marks are about an 1/8 inch apart I would say he used a 1/4 inch bit two flute up spiral, but this is conjecture I cannot prove it.
ok I will back the springs of a little bit(relax)
//chopper

Gerald,

The material I cut was .25" in the picture you have marked.

Thanks, the post above has been edited.

Do you have the transmission plates available?

Stan

I can make them for you if you want or you can build them from the plans
//chopper

these bits are for the cnc machine world like a haas or equivalent,
also onsrud makes some look up there 83-300 series www.onsrud.com
feeds and speed are listed there, I want to throw out a disclaimer here I have done quite a few things to make sure my machine is tight... and backlash free,
without getting into a pissin' match I just want you to know that these cuts may not be accomplished with out the proper modifications to your machine excessive backlash may cause adverse effects like bit breakage etc. and always wear safety glasses, I also want to state that I have an extensive background in metal fabrication / machining / welding etc. which might give me a slight edge on experience in doing this type of work...... and here are a few pics of mild steel 1/8 inch
//chopper

I used a 1/4 inch shank with a 1/4 inch tool dia. the feeds and speeds may very from brand to brand, I used 20 ipm @ .020 cut depth, if you have a machine shop supplier near you or on line with a little looking you will be able to find some that work, just specify that you are doing high speed machining..
the bits I used are from my local supplier and it is there house brand that I used.
//chopper

I hope the above answered your questions also if not please ask I will help with what I can.
//chopper

Chopper, you mentioned "mods" to the MM, what kind of mods (beyond the 4:1 trannies)?

Stan

I modified the Z,
and the rack,
and the spider, but the most important thing is to spend the time to make the machine right, pay attention to the details and tolerances, make sure things are square, and parallel, etc..if you look under my build you can see some of the z and spider mods.
//chopper

That is very nice work chopper.

it has been brought to my attention that the above statement has upset some of you,...the statement I made was in no way meant to be offensive, but I can see how it could be taken that way even though it was not intended to be...( for that I apologize I am very direct and to the point and some times it is taken the wrong way)
all I want to do is show you all what is possible with your machines to think out side the box, to do what they say cannot be done, did I think my machine would cut steel ? or stainless steel? no way but I tried it to see that is all, and to my surprise it did,

as I stated before I have a background in metal fabrication, welding and machining..that allows me to understand what I am doing, and may also give me an edge.. when I was in metal fab we did a lot of work for demanding customers that required perfection, and I have brought those work ethics over into all the work that I do, the mech mate is no different, so what I am saying is the MM is what you make it, if you want to perfect it you can...(from the above posts you can see what is possible), if you do not that is your choice, some will be able to do this and some will not, that I am afraid is a fact, (but the ones who can shouldn't be held back by the ones who can not) and it shouldn't stop you from trying, and as time goes on your understanding will grow and so will your abilities, if you never try you will never know or achieve the impossible,

I also want to say that my belt drives are not the cure all for all the problems that are faced in the building of the MM ( they will not make up for a poorly constructed machine) if you do not spend the time to understand what you are doing or cheap out on parts, or decide that your rails are good enough, or compromise on the quality of your fabrication, you will be limiting your machine.....you and only you can decide what you do, so you can choose to limit yourself or not. but you cannot blame Gerald, myself or anyone else if your machine doesn't preform the way you want after all you built it.. the advise here is given freely you have to decide weather or not you use it and if you do you are responsible for the out come no one else.
with that said all I want to say is good luck on your builds..
//chopper

thanks
//chopper