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Postby gary » Mon Feb 18, 2013 9:25 pm

Harry, you don't seem to have understood what I am saying but you have come, I think, to the right conclusion - it is holding torque that you should be looking for NOT NEMA size.

Please note that the holding torque is a function of power - and power is the product of voltage AND current - so you can have thicker copper (higher current) or better insulation (higher voltage) - IN ANY Nema size within obvious limitations.

The manufacturers do NOT price on NEMA size (although obviously there is more metal and that costs) but on, predominantly, holding torque. Bigger NEMA is NOT necessarily better, particularly if you have a compact installation, it is just a standard size to allow easy interchange independent of manufacture.

You should be looking for the highest holding torque you can afford - as I said, most CNC experts recommend around 200 Oz-in for your size machine (which, being steel, will be heavier than mine and thus harder to move).

But it's all experimental - I found cheap 35 OzIn steppers and they work well enough for cutting acrylic and wood - but VERY slowly compared to most others.
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Postby gary » Mon Feb 18, 2013 9:30 pm

Wonder why there is a jump from the 17 to 23 size .....it also sounds like if they are telling the truth about their motors power rating the wire size is varying depending on who made them ?


I am not sure there is actually - it's just that they are more common - there probably is another size in between - read the NEMA specification if you want more information, especially at bed time as it will put you to sleep in no time at all - as I said it is just a standard physical size to allow easy interchange independent of manufacturer.
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Postby Viewmaster » Tue Feb 19, 2013 1:21 am

harry dalek wrote:
Viewmaster wrote:Harry, other than using bellows or rubber there is another type of coupling that was used on tuning for short wave receivers etc, where zero back lash was essential.
Eddystone Radio made them many years ago and they are seen on ebay
from time to time.
Consisted of a two pieces of brass mounted either side of a circular plate. riveted each side (or use bolts). Coupling boss each side in centre.
The Eddystone one took a 1/4 inch dia shaft.

You could easily make one to suit requirements using 2 pieces of spring steel etc. or something along this principal design.
See piccy of the Eddystone one here.


Hi Albert
I have never seen one of those before made in the days when every thing was hand made i bet .
Is the back the same as the front visa versa ?


Yes Harry, just the same back and front. Each side has a central boss to take the shafts each side. Eddystone couplers were not hand made by the way, but it would be easy to copy this idea.
Bear in mind that one coupler only flexes in one direction. If you need full
flex coverage in all directions then you will need two of 'em.
I reckon that the spiral could be dispensed with and use just two flat pieces
if the flexing is not required to be too great......suck it and see kinda. :)

added......Harry, I don't know how big the loads will be on your rig but you would be welcome to have that Eddystone coupler I showed you, to experiment with.....PM me if you want it.
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Postby Harry Dalek » Tue Feb 19, 2013 3:42 pm

Yes Gary

The motor size did confuse me which isn't hard :oops:

I can see size does not matter but the length and thickness of the wire in them does .

I will look for the 23's i have seen those 175 oz to little over 200 oz so i will be looking for the highest one of those i can get .

The Main motor has to be the strongest ? x Axis i should think i see every one tends to use the same size for all 3 so i am thinking its not a good idea to have 3 different motors with different torques perhaps not good for the controller driver .

I would of thought you have a large or strong motor for the x one a bit smaller for the y and z the smallest just for the amount of mass they would have to move.
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Postby gary » Tue Feb 19, 2013 6:32 pm

Well it's a tricky one that's for sure.

I would be happy with 175 oz-in.

But if you see a really good bargain on 35 oz-in or greater don't let me talk you out of it - slow is better than stopped! and they are useful in other projects down the track anyway so won't be wasted.

I think I could make a good argument that the x and y axis should be the same if possible, but technically they can all be different - the software allows you to make allowances for number of steps max speed etc.

Actually I use a different convention to at least some - I call the longest axis (the one that moves the gantry) the Y and the one that moves the spindle side to side the X, and the one that moves the spindle up and down the Z (I've never seen anyone call the latter anything but Z - although the yanks always mispronounce it zee ;-))
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Postby Harry Dalek » Wed Feb 20, 2013 1:23 pm

gary wrote:Well it's a tricky one that's for sure.


Well i don't really see any one changing the motor size for that so i better no either might be a problem for the controller driver so better copy every one else ...

I would be happy with 175 oz-in.


Again its some thing i would not have thought about till i spoke to you they vary so much but price just a little i again have seen 270s as well in the 23s

But if you see a really good bargain on 35 oz-in or greater don't let me talk you out of it - slow is better than stopped! and they are useful in other projects down the track anyway so won't be wasted.


The 17s all now seem to be 50 up the bagains seem be in this size ,slow is better than nothing i will see what i can find when i get some paypal money in.

I think I could make a good argument that the x and y axis should be the same if possible, but technically they can all be different - the software allows you to make allowances for number of steps max speed etc.



It sounds like there a lot of testing to match your build motors to the software which is understandable.

Actually I use a different convention to at least some - I call the longest axis (the one that moves the gantry) the Y and the one that moves the spindle side to side the X, and the one that moves the spindle up and down the Z (I've never seen anyone call the latter anything but Z - although the yanks always mispronounce it zee ;-))



It just seems right the x bottom y next up and z last i suppose its where you first learned the movemnets from .

Down here in victoria they say castle as in usa speak drives me nuts they may be right due to the spelling is that way i love to correct them oh you mean Carstle.

I am working on the Z movement today so out comes the tape measure and angle grinder .
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Postby gary » Wed Feb 20, 2013 4:58 pm

It sounds like there a lot of testing to match your build motors to the software which is understandable.


Actually no - the only thing that is trial and error is determining the maximum speed the steppers can travel at without losing steps - after that it is just a matter of plugging the numbers in.
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Postby Harry Dalek » Wed Feb 20, 2013 9:18 pm

Actually no - the only thing that is trial and error is determining the maximum speed the steppers can travel at without losing steps - after that it is just a matter of plugging the numbers in.


Good to be wrong on this least amount of that the better i say !

Have you found vibration to be a problem from your cutting motor ?

Perhaps the slow steppers or running them slow might be a good thing for fine work ?
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Postby gary » Wed Feb 20, 2013 9:44 pm

harry dalek wrote:Have you found vibration to be a problem from your cutting motor ?


No, not at all. That would indicate a problem with the spindle (if my assumption that "cutting motor" is the spindle is correct).

harry dalek wrote:Perhaps the slow steppers or running them slow might be a good thing for fine work ?


the speed is something associated with the cutter and the material being cut - this is a minor science in itself and is way too complicated to go into here - suffice it to say that is something you will learn along the journey, but it is the same knowledge you need to know whether you are doing it manually or via CNC.

In regards to accuracy of the positioning of the cutter then all things being equal (i.e. no racking no flexing) then as long as steps aren't missed speed has nothing at all to do with it.
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Postby Harry Dalek » Fri Feb 22, 2013 2:25 pm

No, not at all. That would indicate a problem with the spindle (if my assumption that "cutting motor" is the spindle is correct).


i am not sure what to expect but hope all gos well .


the speed is something associated with the cutter and the material being cut - this is a minor science in itself and is way too complicated to go into here - suffice it to say that is something you will learn along the journey, but it is the same knowledge you need to know whether you are doing it manually or via CNC.In regards to accuracy of the positioning of the cutter then all things being equal (i.e. no racking no flexing) then as long as steps aren't missed speed has nothing at all to do with it.



Oh yes like the difference in cutting wood and steel and how good the cutting tool is ....
I am trying to make it as strong as i can .

I still have not finished the Z part almost there ...i pulled a lot of it to bits and put it back together for i wanted the cutting space a little higher just incase and save me work in the future ....

Also needed to get the rail of the Y welded inplace i had it bolted but wasn't happy with that idea.

I am starting to see it might very well do what i want it might not be the prettiest one but :wink:
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Postby gary » Fri Feb 22, 2013 2:33 pm

That's quite an unusual arrangement you have there Harry, most unconventional. I am a bit worried that after you attach the spindle (what ever that will be) that it's centre of gravity may not be ideal - possibly causing racking. OTOH being built of steel it may well be fine - I guess you will eventually find out.
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Postby Harry Dalek » Fri Feb 22, 2013 3:03 pm

gary wrote:That's quite an unusual arrangement you have there Harry, most unconventional. I am a bit worried that after you attach the spindle (what ever that will be) that it's centre of gravity may not be ideal - possibly causing racking. OTOH being built of steel it may well be fine - I guess you will eventually find out.



It seems pretty strong i am not sure i could get a router onit i would be happy if my like dremel works so its over sized for that .

The L bracket used in the Z would hold up a house ...all the weak points are really the bearings connecting to the rails so long as they hold up and the bearings brackets i should be right ...i have the basic i idea of the thing now .

To make it any stronger and if i was good at drilling i would of used better thicker Angle steel but i am not so any thing that needs to be spot on for a hole i have gone with predrilled least i have a little skill at welding that helps the rest.

I am pretending it a big meccano set :wink:


The size of the Z rails are really a bit long but i just rather long than to short to adjust it for now its just going to be a copy of the other rails ugly as ....but i know how to make those so it will be a massive Z . :shock:
Last edited by Harry Dalek on Fri Feb 22, 2013 7:10 pm, edited 1 time in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Fri Feb 22, 2013 3:38 pm

Oh Harry - it looks very strong and well built - but you know the old adage - give me a lever and I will move the earth - the trick with these systems is to balance the loads and stresses so that the forces on the bearings are compressive (where they are very strong) rather than lateral where they are weaker - the forces should be pushing the bearings onto the rails as much as possible rather than away from them or worse still sideways. If that is achieved then the arrangement you have will be virtually indestructible.
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Postby Harry Dalek » Fri Feb 22, 2013 4:43 pm

gary wrote:Oh Harry - it looks very strong and well built - but you know the old adage - give me a lever and I will move the earth - the trick with these systems is to balance the loads and stresses so that the forces on the bearings are compressive (where they are very strong) rather than lateral where they are weaker - the forces should be pushing the bearings onto the rails as much as possible rather than away from them or worse still sideways. If that is achieved then the arrangement you have will be virtually indestructible.


OH i see what you mean i am pushing out to much for the z direction.this will lever the Y bearings away from the rail when your cutting tool works ...I think or twist the rail a bit what ever gives first. ...should have done the Y rails bearings perhaps on the vertical that way the force would be pushing against the the rail equal.

I will have a think about it unbolting day twist the y rail to point up and down instead of side ways horizontal and redo it !

Good advice i will redesign Gary
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Postby Viewmaster » Fri Feb 22, 2013 6:26 pm

That 'carriage',shall we call it Harry, with the bearings at 45 degree each side. What is the system to prevent any upward /sidewise rock movements?

What bearing/restrainers are underneath the track to prevent this? (I may have missed this on previous photos)
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