My CNC Router Build Adventure

[peteeng]

Hi All - Re motor at front. 1) Putting the motors at the back is an issue if the machine is to be pushed up against a wall which its likely to be. Takes up quite a bit of space 2) I have not noticed the motors "sticking" out the front. They are nearly within the footprint as I left space at the front of bed for long objects to be paced across the machine. 2 people have used the machine and have not commented that they have been a problem as they move around the machine. 3) Since the gantry is driven by two motors you can use a short motor. I typically use all the same motors so I can swap them around if I have to but for the dual drive you could use 2x 75mm long motors vs a 112mm long to save the "stick out" if its a real issue... Peter

[mactec54]

Hi All - Re motor at front. 1) Putting the motors at the back is an issue if the machine is to be pushed up against a wall which its likely to be. Takes up quite a bit of space 2) I have not noticed the motors "sticking" out the front. They are nearly within the footprint as I left space at the front of bed for long objects to be paced across the machine. 2 people have used the machine and have not commented that they have been a problem as they move around the machine. 3) Since the gantry is driven by two motors you can use a short motor. I typically use all the same motors so I can swap them around if I have to but for the dual drive you could use 2x 75mm long motors vs a 112mm long to save the "stick out" if its a real issue... Peter

If they did not stick out very much, then at the Back would not of been a problem.

You would never have a machine like this against a wall. so that is a bad excuse for this design. you need to be able to get around a machine like this, which goes for almost all types of 3/4 Axis CNC Machines, not just yours.

[JayneV]

Putting the motors inside the frame is a good idea, I never do it any other way. even for direct drive, doing it the way Peter did having the motors out the front gets old fast, I said in one of his posts to at least put them out the back of the machine, if you have to direct drive like this.

Just so you have more information on Belts Drives, you will see in this snip, that Trapezoidal Tooth Timing belts are at the bottom of the list of Belts to use for CNC machine drives.

PTparts have HTD Timing Belts listed, this was the improved design over the Trapezoidal tooth design, the GT series came after the HTD, if you decide on something to use I will help with the part numbers, if you have a problem with that part, as even in this snip they have some confusing code numbers for some of the Belts series listed

Hi Mactec,

I had typed out a response on my phone and was ready to send it when my decided to have a moment and lost everything I typed, so here goes round two. lol

If I were to mount the motors outside the frame, they would be out the back like they were on earlier versions of Carlos, but I really like them located inside the frame.

Thank you for the snip of information you attached. Where is that sourced from? I have seen conflicting information about the suitability of HTD vs trapezoidal tooth profiles in precision positioning applications. Up until recently I thought that a toothed belt was a toothed belt with the only differences being in the width and the type of material used to make it. It has been very educational but can get confusing for a newbie like me. I have circled statements in the attached documents that seem to suggest that HTD is less precise than trapezoidal if I have understood correctly?

ptparts responded to my email earlier today with much more information than their previous reply. They quoted for AT5 belts and attached some calcs (see attached) which I still need to read through. The other supplier also replied with a short email giving prices and part numbers, see below in italics.

Thank you for your enquiry, please see pricing below
1 x 340-5M-15 timing belt @ $20.90 + GST 1-2 Days Delivery
1 x 400-5M-15 timing belt@ $22.40 + GST 1-2 Days Delivery
2 x 24-5M-15 timing pulley @ $11.50 Each + GST 1-2 Days Delivery
DELIVERY @ $20 + GST


From the part numbers, they look like HTD belts. I sent them a reply asking to confirm the belt type.

[JayneV]

Hi All - Re motor at front. 1) Putting the motors at the back is an issue if the machine is to be pushed up against a wall which its likely to be. Takes up quite a bit of space 2) I have not noticed the motors "sticking" out the front. They are nearly within the footprint as I left space at the front of bed for long objects to be paced across the machine. 2 people have used the machine and have not commented that they have been a problem as they move around the machine. 3) Since the gantry is driven by two motors you can use a short motor. I typically use all the same motors so I can swap them around if I have to but for the dual drive you could use 2x 75mm long motors vs a 112mm long to save the "stick out" if its a real issue... Peter

If they did not stick out very much, then at the Back would not of been a problem.

You would never have a machine like this against a wall. so that is a bad excuse for this design. you need to be able to get around a machine like this, which goes for almost all types of 3/4 Axis CNC Machines, not just yours.

Hi everyone,
My machine will sort of be located against a wall, except part of that wall is actually a garage roller door leading out to our back yard. It's the only place I can fit the machine, but any other location would be up against a wall anyway, due to space limitations. I'd love to have room to spare to get all around the machine, but unfortunately that is not the case. However, I'm leaning very much towards the motors being inside the frame, so whether motors stick out the front or back is no longer something to worry about.

The machine will also be mounted in line with the front edge of the bench to allow clamping workpieces to the front face of the bench to machine on the edge. I'm thinking of attaching a length of t-slot extrusion, around 200mm wide to the front face of the bench to secure work pieces. That would be one of those nice to have features to include for minimal additional cost.

Jayne

[mactec54]

Hi Mactec,

I had typed out a response on my phone and was ready to send it when my decided to have a moment and lost everything I typed, so here goes round two. lol

If I were to mount the motors outside the frame, they would be out the back like they were on earlier versions of Carlos, but I really like them located inside the frame.

Thank you for the snip of information you attached. Where is that sourced from? I have seen conflicting information about the suitability of HTD vs trapezoidal tooth profiles in precision positioning applications. Up until recently I thought that a toothed belt was a toothed belt with the only differences being in the width and the type of material used to make it. It has been very educational but can get confusing for a newbie like me. I have circled statements in the attached documents that seem to suggest that HTD is less precise than trapezoidal if I have understood correctly?

ptparts responded to my email earlier today with much more information than their previous reply. They quoted for AT5 belts and attached some calcs (see attached) which I still need to read through. The other supplier also replied with a short email giving prices and part numbers, see below in italics.

Thank you for your enquiry, please see pricing below
1 x 340-5M-15 timing belt @ $20.90 + GST 1-2 Days Delivery
1 x 400-5M-15 timing belt@ $22.40 + GST 1-2 Days Delivery
2 x 24-5M-15 timing pulley @ $11.50 Each + GST 1-2 Days Delivery
DELIVERY @ $20 + GST


From the part numbers, they look like HTD belts. I sent them a reply asking to confirm the belt type.

The proof is is what is used in the CNC manufacturing, the very first CNC machines used a trapezoidal tooth designed belt, for Axis drives, because that's all there was, next came the HTD which is still used today in some CNC machines, then the GT series was developed to what it is today

1940s Trapezoidal tooth Belts
1971 HTD was introduced
1985 GT series was introduced

Yes the HTD can have more Backlash than the AT Belts, only if the Timing Pulleys are a small diameter, overall the 2 profile types have around the same Backlash, if used with the correct size Timing Pulleys, the HTD run smoother and are quieter that an AT Belt, so this HTD will always be a better choice than the AT series, and then you have the GT-3 which is the best in all areas, but not locally easy for you to get.

So what ever is available for you will work, it is not so difficult to choose something that is local that will work for you, if the Timing pulleys can only be a small diameter, then AT Belt would be best. as the HTD will have more Backlash when using a Small Diameter Timing Pulley.

[mactec54]

Hi Mactec,

I had typed out a response on my phone and was ready to send it when my decided to have a moment and lost everything I typed, so here goes round two. lol

If I were to mount the motors outside the frame, they would be out the back like they were on earlier versions of Carlos, but I really like them located inside the frame.

Thank you for the snip of information you attached. Where is that sourced from? I have seen conflicting information about the suitability of HTD vs trapezoidal tooth profiles in precision positioning applications. Up until recently I thought that a toothed belt was a toothed belt with the only differences being in the width and the type of material used to make it. It has been very educational but can get confusing for a newbie like me. I have circled statements in the attached documents that seem to suggest that HTD is less precise than trapezoidal if I have understood correctly?

ptparts responded to my email earlier today with much more information than their previous reply. They quoted for AT5 belts and attached some calcs (see attached) which I still need to read through. The other supplier also replied with a short email giving prices and part numbers, see below in italics.

Thank you for your enquiry, please see pricing below
1 x 340-5M-15 timing belt @ $20.90 + GST 1-2 Days Delivery
1 x 400-5M-15 timing belt@ $22.40 + GST 1-2 Days Delivery
2 x 24-5M-15 timing pulley @ $11.50 Each + GST 1-2 Days Delivery
DELIVERY @ $20 + GST


From the part numbers, they look like HTD belts. I sent them a reply asking to confirm the belt type.

They are the AT5 Belts and pulleys that they have quoted 16 AT5/375

Look up the Timing Pulley sizes and see if it can be bored out to the size you need, and still have enough left on the boss for the Grub screws and Key if you are using one, they have taper lock Timing Pulleys available also, this may be a better choice for you to look at, as you may get lucky that they have the Taper Lock bushings for the size you need.

[JayneV]

Hi Mactec,
The second supplier responded confirming they quoted for HTD belts, that is is the one with the xxx-5M-15 part numbers in my earlier email. So to clarify, I have one quote for AT5 and one for HTD.

Yes, the pulleys can be bored out to the size I need. Their data sheets quote the maximum bore size for each size pulley and the ones I need have a maximum bore well above the shaft sizes of the motor and screw. Thanks for pointing that out though.

Out of interest, does it matter if the pulleys have an even or odd number of teeth? I might be over thinking this, but the reason I ask is with an even number of teeth, the tooth engagement on the leading and trailing sides of the pulley would be symmetrical. Since the belt will constantly be changing direction, is it desirable to have symmetrical tooth engagement on both sides of the pulley, or doesn’t it matter? I was planning to use 25T pulleys but can go with 24T or 26T if an even number is better.

Jayne

[davida1234]

Interesting thought....

[peteeng]

Hi Jayne - I don't think that matters. Say you use the 25T and assume the first 4 teeth are transferring the load. Then that means the lead 4 and lag 4 are loaded (12.5T for 180deg wrap) so the "middle 4.5T are unloaded) doesn't matter if it was 5T or 20T in the dead zone) as long as there is a dead zone then backlash is minimised or zero if preload is correct. If you used a 16T or less pulley then the lag and lead teeth would interact and the tooth clearance at change of direction would become an issue... Peter

[JayneV]

Hi Peter, I understand the dead zone area of the pulley not mattering as long as the pulley has enough teeth for the lead and lag sides not to overlap, I'm referring only to the lead and lag side of the pulley. If the pulley has an odd number of teeth the symmetry of the pulley between the lead and lag tooth engagement will not be matched because at any point in time during rotation one side would be half a tooth out of alignment with the other side. See attached image showing an 18T pulley to help illustrate what I am trying to say. (ignore the dimension lines, the image is lifted from the Optibelt manual) Again, I am probably way overthinking this.

Jayne

[mactec54]

Hi Mactec,
The second supplier responded confirming they quoted for HTD belts, that is is the one with the xxx-5M-15 part numbers in my earlier email. So to clarify, I have one quote for AT5 and one for HTD.

Yes, the pulleys can be bored out to the size I need. Their data sheets quote the maximum bore size for each size pulley and the ones I need have a maximum bore well above the shaft sizes of the motor and screw. Thanks for pointing that out though.

Out of interest, does it matter if the pulleys have an even or odd number of teeth? I might be over thinking this, but the reason I ask is with an even number of teeth, the tooth engagement on the leading and trailing sides of the pulley would be symmetrical. Since the belt will constantly be changing direction, is it desirable to have symmetrical tooth engagement on both sides of the pulley, or doesn’t it matter? I was planning to use 25T pulleys but can go with 24T or 26T if an even number is better.

Jayne

It does not matter to much about tooth count, quite often odd teeth Timing Pulleys are special order, so these may not be available, the only thing is the tooth belt engagement the more the better, so if you have room for the 26 use them, these Timing Pulleys are too small for the HTD, the Backlash will be more with the HTD with this size Timing Pulley, so it is an easy choice with what you have available

[peteeng]

Hi Jayne - Yes too many thought bubbles from your champagne. There still is a leading and lagging tooth even though its half tooth out geometrically. Time to commit to an solution and move on. Peter

[mactec54]

Hi Peter, I understand the dead zone area of the pulley not mattering as long as the pulley has enough teeth for the lead and lag sides not to overlap, I'm referring only to the lead and lag side of the pulley. If the pulley has an odd number of teeth the symmetry of the pulley between the lead and lag tooth engagement will not be matched because at any point in time during rotation one side would be half a tooth out of alignment with the other side. See attached image showing an 18T pulley to help illustrate what I am trying to say. (ignore the dimension lines, the image is lifted from the Optibelt manual) Again, I am probably way overthinking this.

Jayne

I have never looked a it like this, it still would not matter, I have used odd number Timing Pulleys and made them, Have not seen a problem, I made a 13 tooth large pitch Timing Pulley for a 2 :1 Drive it worked normal

[JayneV]

Thank you Mactec and Peter, for throwing a lifeline to save me from an overthinking brain explosion.

I've just been comparing prices between local suppliers and Powge at AliExpress. Local supplier prices vary from $168 to $295, although that is not apples to apples because one place (the $168 price) quoted me for HTD and the other two are for AT5 belts. Powge only sell AT5 pulleys as a custom order with a minimum qty of 10. Ordering 10 pulleys and 3 belts from them comes to $163. I also checked HTD belts from powge, which are not a custom order and that came to around $80. They have a large range of sizes available in the HTD range making it easy to select the exact size I want. What would be the minimum pulley size to avoid backlash with a HTD belt? The X axis is not a problem, there is enough space to choose any size pulley, but the Y axis will need some adjustments to be made depending how big the pulley is due to a potential clash between the pulley and structure.

Jayne

[mactec54]

Thank you Mactec and Peter, for throwing a lifeline to save me from an overthinking brain explosion.

I've just been comparing prices between local suppliers and Powge at AliExpress. Local supplier prices vary from $168 to $295, although that is not apples to apples because one place (the $168 price) quoted me for HTD and the other two are for AT5 belts. Powge only sell AT5 pulleys as a custom order with a minimum qty of 10. Ordering 10 pulleys and 3 belts from them comes to $163. I also checked HTD belts from powge, which are not a custom order and that came to around $80. They have a large range of sizes available in the HTD range making it easy to select the exact size I want. What would be the minimum pulley size to avoid backlash with a HTD belt? The X axis is not a problem, there is enough space to choose any size pulley, but the Y axis will need some adjustments to be made depending how big the pulley is due to a potential clash between the pulley and structure.

Jayne

28 and up will work with the HTD, always being more teeth engagement the better, so go as big as you can fit if you want to use the HTD

[JayneV]

Hi everyone,

I've been playing with different size pulleys and motor position for the Y axis to figure out what will work. 28T pulleys will fit without too much modification, only need to move the motor mount slightly outboard and up (see attached image). The green bracket to the right of the belt has clearance behind the belt and does not interfere as it appears in the image. I could go up to 32T pulleys but clearance between the top pulley and the top plate where the linear bearing is mounted gets a bit close requiring everything to be shifted outboard (motor, ballscrew & ballnut bracket).

The pulley models in the drawing were downloaded from the Misumi website, configured as 28T-AT5 type. The dimensions are almost identical to the HTD type so they are good enough for modelling purposes. HTD belts seem to be very cheap and available everywhere, so I'll start with them and if they don't work then I can get something different down the track. I will probably place an order tomorrow, that way I will have committed to something so I can move on.

The next question I have is about the end machining on the ballscrew. The standard end machining that BST Motion supply for a 16mm ballscrew has dimension "F" (see attachment) equal to 15mm. For 16mm wide belts, AF pulleys have an overall width of 20mm and the BF style have a width of 30mm. Both the AF and BF pulleys will partially overhang the end of the ballscrew shaft. The set screws on the BF pulleys would be better located further in from the end of the shaft than the AF pulley set screws, but the BF would have almost the full width of the toothed section overhanging the end.

Is a certain amount of overhang acceptable or should I be asking for custom machined ends on the ballscrews? I'd like to avoid any custom machining if possible to keep costs down and for easier part replacement in the future. A 20mm ballscrew has a larger dimension "F" (20mm) which would eliminate the overhang issue using AF pulleys. Sometimes I think I'm chasing my tail with these belt drives.

[mactec54]

Hi everyone,

I've been playing with different size pulleys and motor position for the Y axis to figure out what will work. 28T pulleys will fit without too much modification, only need to move the motor mount slightly outboard and up (see attached image). The green bracket to the right of the belt has clearance behind the belt and does not interfere as it appears in the image. I could go up to 32T pulleys but clearance between the top pulley and the top plate where the linear bearing is mounted gets a bit close requiring everything to be shifted outboard (motor, ballscrew & ballnut bracket).

The pulley models in the drawing were downloaded from the Misumi website, configured as 28T-AT5 type. The dimensions are almost identical to the HTD type so they are good enough for modelling purposes. HTD belts seem to be very cheap and available everywhere, so I'll start with them and if they don't work then I can get something different down the track. I will probably place an order tomorrow, that way I will have committed to something so I can move on.

The next question I have is about the end machining on the ballscrew. The standard end machining that BST Motion supply for a 16mm ballscrew has dimension "F" (see attachment) equal to 15mm. For 16mm wide belts, AF pulleys have an overall width of 20mm and the BF style have a width of 30mm. Both the AF and BF pulleys will partially overhang the end of the ballscrew shaft. The set screws on the BF pulleys would be better located further in from the end of the shaft than the AF pulley set screws, but the BF would have almost the full width of the toothed section overhanging the end.

Is a certain amount of overhang acceptable or should I be asking for custom machined ends on the ballscrews? I'd like to avoid any custom machining if possible to keep costs down and for easier part replacement in the future. A 20mm ballscrew has a larger dimension "F" (20mm) which would eliminate the overhang issue using AF pulleys. Sometimes I think I'm chasing my tail with these belt drives.

Looks like you have more thread than you need, you could machine some of the thread, to give you more for the pulley, what I do when machining the Ballscrew ends, is drill and tap the end, and add a machined top-hat, that locates in the pulley and clamps the whole assembly together, preloading the Bearings, as well as holding the pulley in place, no Bearing Lock-Nut used, just a spacer, as per the snips.

[JayneV]

Hi Mactec,
If you are referring facto the excess thread between the beating and pulley, that may be a result of mating the ballscrew and the bearing in CAD. I don’t actually know how much thread will be exposed past the bearing locknut. The red arrow in the image was attempting to show the pulley seated right up against the threaded section of the ballscrew where the shaft diameter steps down for the pulley.

I think I understand what you tried to explain and what you are showing with the pictures. It looks like a nice solution. Perhaps I’ll do that in a future project, I prefer not to do any machining to the ballscrews if possible for a first build. What is the part that sort of looks like a jigsaw blade in the last image?

[mactec54]

Hi Mactec,
If you are referring facto the excess thread between the beating and pulley, that may be a result of mating the ballscrew and the bearing in CAD. I don’t actually know how much thread will be exposed past the bearing locknut. The red arrow in the image was attempting to show the pulley seated right up against the threaded section of the ballscrew where the shaft diameter steps down for the pulley.

I think I understand what you tried to explain and what you are showing with the pictures. It looks like a nice solution. Perhaps I’ll do that in a future project, I prefer not to do any machining to the ballscrews if possible for a first build. What is the part that sort of looks like a jigsaw blade in the last image?

Then ask the manufacture to make the Pully mounting length longer on the Ballscrew.

[JayneV]

Then ask the manufacture to make the Pully mounting length longer on the Ballscrew.

Ok, that was basically my question. So the pulley should not have any overhang from the end of the shaft, the pulley mounting part of the ballscrew should be long enough to match the width of the pulley? I’ll send a message to BST asking if they offer this service. Thanks for the info.