My CNC Router Build Adventure

[peteeng]

Hi Jayne - ideally there should be no overhang but a small overhang is OK if you go std end detail. BST will custom machine ends. I have done this before. You need to supply a detailed manufacturing drawing to them. Also since you know what you want in regard to belts and pulleys you can ask Fred if he will source them for you. If he can he will quote and then you can consolidate the parts to BST. He has supplied parts to me that are not on their std products list before... The jigsaw blade is a broach used to cut the key slot....Peter

[JayneV]

Hi Peter,
Makes sense to have no overhang or only a small amount. I’ll make a drawing and send a message to Fred today. Good idea about also asking him about belts and pulleys. If I go with custom machined ends, is it worth asking for a key slot or a flat for a more positive engagement with the pulley, and then get pulleys to suit?

Ah, thanks for identifying the broach, I haven’t seen one before.

[peteeng]

Hi Jayne - I do not know the extent that BST will do "custom" eg they may not do slots. Fred will say no if they don't do this. No harm in asking do a dwg for what you want and see if it flies or not. I haven't used keyways in this application before. Setscrews and loctite is the usual for me... or in other situations I prefer taperlocks. Strong adjustable doesn't damage shaft... Peter

[JayneV]

Thanks Peter. I’ll get to work on the drawing.

[mactec54]

Hi Jayne - I do not know the extent that BST will do "custom" eg they may not do slots. Fred will say no if they don't do this. No harm in asking do a dwg for what you want and see if it flies or not. I haven't used keyways in this application before. Setscrews and loctite is the usual for me... or in other situations I prefer taperlocks. Strong adjustable doesn't damage shaft... Peter

Only a hack will screw direct onto a shaft, even with flats on the shaft, with grub screws / set screws, it still is not correct, it takes nothing to add a key, or use a taper-lock, if these are available in the sizes that are needed for the build, taper locks also need a key some times, depending on the load.

What you do is your business, you should not be proud to do it like that, and post like it is the norm, Engineer's don't do things like this

[mactec54]

Thanks Peter. I’ll get to work on the drawing.

You should send the drawing in PDF. format this way there is no confusion on the other end.

[peteeng]

Hi M54 - I did neglect to say that if screws are used flats are required for the screws. Unfortunately everything can't be explained in detail in this sort of thread.... Peter

[JayneV]

Hi everyone,

I've been working on some of the details on Carlos, checking fits and clearances and adding things like bolt holes to make sure there are no clashes. One of the items on my to do list has been to find a simple way to tension the drive belts. I came across a design on thingiverse which I liked, so I based the tensioning mechanism for the Y axis on that design. The X axis had less room, so I went a different route with that. I thought an adjusting screw that performs double duty as a nut for the motor mounting bolts might work. See attached images.

I also received a reply from Fred at BST motion. I am happy with the price he gave me for the ballscrews with custom end machining, end supports, ball nuts, etc. as well as all the linear rails and cars. Soon as I triple check all the dimensions, I will place an order. Fred is also able to machine a flat on the shaft end for the pulley if I end up using regular pulleys with set screws. I am still looking for suitable taper lock pulleys at an affordable price. So far this is what I have been able to find https://www.aliexpress.com/item/3289...35c72d97BAZvEK. Has anybody dealt with this vendor before? The shipping costs are twice the cost of the pulley, but the total price is still ok. Are there any other vendors anyone can suggest?

[mactec54]

Hi M54 - I did neglect to say that if screws are used flats are required for the screws. Unfortunately everything can't be explained in detail in this sort of thread.... Peter

Even with a flat it is not a satisfactory drive for a Ballscrew Drive, the impulse loading, which you get with CNC drives, the 2 small points of a setscrew, is not enough to stop any movement that will occur.

[JayneV]

Hi Mactec,
Thank you for the attachments. Most of the Nema 23 motor shafts seem to come with a flat on the shaft instead of a key slot (I’ll do some more searching). Assuming the motor pulley is experiencing the same loads as the ballscrew pulley (same size pulleys), would I be correct in saying that both pulleys should use the same method of securing to the shaft?

Would you use a taper lock like the one in the attached image on a shaft without a key? I don’t want to be machining the motor shafts and it seems pointless to use a key on the ballscrew and not on the motor, if I am understanding correctly.

[peteeng]

hi Jayne - Loctite solves most/all of those issues. Peter

[davida1234]

hi Jayne - Loctite solves most/all of those issues. Peter

As a (usually) permanent solution. You will probably damage the aluminum pulley should you ever try to pull the pulley off the shaft.

[peteeng]

Hi David - Only if you use a high strength version. Also if you warm the pulley with a heat gun it will come off . Peter

[JayneV]

Ah yes! You did mention loctite previously, Peter. It slipped my mind, thanks for the reminder. Taper locks seem like a better option. I think I will go with taper locks if I can find the size I need at a reasonable price and keep the plain pulleys with loctite as plan B.

[JayneV]

Peter, out of interest and if I end up going that route, which type of loctite do you use on the pulleys?

[peteeng]

Hi Jayne - I have used all sorts and they all work. High strength (like 277) obviously is very good. Its not as strong on aluminium and if you have pulley pullers it will come off. Medium strength is good... But I like wicking types as you can set up the pulley how you want then put a drop on the side and set the assembly. This means you don't need to assm and mark, pull it down, add adhesive, reassemble and set. This is Loctite 290. Other brands have equivalent types Permatex is good to. Stepper motors create a lot of vibration and pulleys do come loose and they are hard to diagnose sometimes. Since using threadlockers/retainers I haven't had one come loose.

https://www.permatex.com/products/th...-relaxed-fits/

https://www.permatex.com/product-cat...threadlockers/

https://www.repco.com.au/en/car-care...20a/p/A7780133

[peteeng]

Hi Jayne - medium strength lockers have a strength of about 5MPa in shear, high strength are aboye 10 and epoxy is about 30Mpa for those really tough cases. Did a quick calc on a 10mm shaft and a 3Nm motor places the bondline in about 1.2MPa stress so there's quite a reserve in the strength. An M10 bolt requires 5Nm to break it free so again thats more then the motors can produce unless its a crash case. Peter

[JayneV]

Hi Jayne - I have used all sorts and they all work. High strength (like 277) obviously is very good. Its not as strong on aluminium and if you have pulley pullers it will come off. Medium strength is good... But I like wicking types as you can set up the pulley how you want then put a drop on the side and set the assembly. This means you don't need to assm and mark, pull it down, add adhesive, reassemble and set. This is Loctite 290. Other brands have equivalent types Permatex is good to. Stepper motors create a lot of vibration and pulleys do come loose and they are hard to diagnose sometimes. Since using threadlockers/retainers I haven't had one come loose.

https://www.permatex.com/products/th...-relaxed-fits/

https://www.permatex.com/product-cat...threadlockers/

https://www.repco.com.au/en/car-care...20a/p/A7780133

Hi Peter,

Thank you, this is very helpful information.

[JayneV]

Hi Jayne - medium strength lockers have a strength of about 5MPa in shear, high strength are aboye 10 and epoxy is about 30Mpa for those really tough cases. Did a quick calc on a 10mm shaft and a 3Nm motor places the bondline in about 1.2MPa stress so there's quite a reserve in the strength. An M10 bolt requires 5Nm to break it free so again thats more then the motors can produce unless its a crash case. Peter

Oh wow! I had no idea loctite worked so well. It gives me a whole new appreciation for its effectiveness. The 290 data sheet mentions Breakaway Torque(10Nm) and Breakloose Torque(30Nm). What is the difference between those two terms?

[mactec54]

Hi Mactec,
Thank you for the attachments. Most of the Nema 23 motor shafts seem to come with a flat on the shaft instead of a key slot (I’ll do some more searching). Assuming the motor pulley is experiencing the same loads as the ballscrew pulley (same size pulleys), would I be correct in saying that both pulleys should use the same method of securing to the shaft?

Would you use a taper lock like the one in the attached image on a shaft without a key? I don’t want to be machining the motor shafts and it seems pointless to use a key on the ballscrew and not on the motor, if I am understanding correctly.

No the correct way, is to either have a round shaft, to use a Taper-Lock or a shaft with a key

A taper- lock normally likes a round shaft, because your shafts are so small, you don't have very much surface area, so even if you have a flat on the stepper motor you can still make a key that can fit in that small space and the Timing pulley which is showing a key in the taper-lock, this is still better than no key in the shaft, if you have the options to use a key then do your best to use it, as Peter has said Loctite can solve some of these problems, but when you have Ballscrew thrust Bearing that may need adjusting, then you don't want to be dealing with a pulley that has used Loctite to keep it in place, with a Taper-Lock also you would not normally use Loctite on them