[JayneV]

I am maintaining another build thread for this machine over on a guitar forum but that is just a condensed version where I only post major updates on my progress. One of the comments I received on that thread was about the extra weight of the z axis when it is configured with the rails, screw, stepper motor and spindle all mounted on the z plate compared with the motor, rails and screw mounted on the saddle. I know machines exist with both configurations. My gut feeling tells me a 3Nm stepper coupled to a 5mm pitch screw will be able to handle the weight and a brake will hold the axis in place when the motor is unpowered. It seems this design could benefit from some type of counterbalance for the z axis. Are counterbalance devices often used as a design feature or are they usually added as an afterthought to improve a less than optimal design?

Jayne

[mactec54]

I am maintaining another build thread for this machine over on a guitar forum but that is just a condensed version where I only post major updates on my progress. One of the comments I received on that thread was about the extra weight of the z axis when it is configured with the rails, screw, stepper motor and spindle all mounted on the z plate compared with the motor, rails and screw mounted on the saddle. I know machines exist with both configurations. My gut feeling tells me a 3Nm stepper coupled to a 5mm pitch screw will be able to handle the weight and a brake will hold the axis in place when the motor is unpowered. It seems this design could benefit from some type of counterbalance for the z axis. Are counterbalance devices often used as a design feature or are they usually added as an afterthought to improve a less than optimal design?

Jayne

A lot of builders use a gas strut, like what is used on auto's Etc. I agree with what they are saying also, it is not normal for the motor and screw to move with the Z axis, any gain from using this design is lost with the extra moving weight

[davida1234]

I did a bit of research about gas struts when I was designing my machine (David A's Desktop Version 2).

According to major US gas strut manufacturers, a gas strut is a high friction device and is not designed for continued operation as continued friction creates heat.

They are more appropriate for single movements like lifting a hood or tail gate and have defined life spans.

I chose simple extension springs for my machine.

[peteeng]

Hi Jayne - I have used gas struts and they work but they can consume stroke once you figure out bracketry. Some people disagree with the moving motor concept but I have used it on two machines with no issues. Usual concern is extra weight but then the motors job is to lift weight and they do this easily.

Balancing the Z is either 1) to prevent it from falling when there is no power or 2) to improve its dynamics if it is a fast moving machine. The Z axis is rarely fast moving so 2) can be moot. A 3Nm motor at 500rpm (ie its moving at 2500mm/min which is really fast for a Z) with a 5mm pitch screw can produce 173kgf. This is more then enough force to lift your Z axis. At slow speeds it has over 300kgf so even better for plunging into material. To prevent the axis falling I now use an electric motor brake. On my current machine its worked very well. No stroke lose, reliable and simple. By the time you add up the cost of springs, gas struts, brackets nuts and bolts the integrated brake is same cost... maybe cheaper... Peter

re gas struts - as David explained they are for slow applications. They have an internal damper otherwise your tailgate would fly up and crash into its stops every time you opened it. You can hear the squelch as it operates. This damper dissipates heat. But then a damper on the Z was good on my belt drive Z it behaved very smoothly. One issue with the strut is that its stated force is not its actual force due to poor manufacturing tolerances. I bought one at a truck place on its spec got it home and found it was twice the stated spec so overpowered the axis. So I took my bath scales back to the shop sat on the floor and went through a whole pigeon hole full of struts before I found one at the right spec... as expected it was the second last one that was good.

You mention guitar parts and I recommend you have at least 200mm for your Z. Guitar bodies are thick and you will need a fixture underneath and I expect a 125-150mm Z will be too small...

[mactec54]

I did a bit of research about gas struts when I was designing my machine (David A's Desktop Version 2).

According to major US gas strut manufacturers, a gas strut is a high friction device and is not designed for continued operation as continued friction creates heat.

They are more appropriate for single movements like lifting a hood or tail gate and have defined life spans.

I chose simple extension springs for my machine.

There are people here on the Zone that have been using Gas strut's for years without any problems, some are using a regular air cylinder which works very well also, with an air cylinder you can control the load in both directions, your springs, will have more loading, as you stretch them out, so don't have any consistency over the travel of the axis, a Gas strut does and an air cylinder you can adjust to suit your machine needs.

[JayneV]

Hi everyone,

Thank you for the feedback re Z axis support. The reason I chose a moving motor setup for the Z axis was to achieve a better compromise between large Z capacity while still having enough stiffness to cut aluminium. I got the idea from another build thread here on the forum. The idea is when the Z plate is fully extended, there will be a larger cantilever but the cantilever will be less when the z axis is raised. See sketches (1) and (2) in the attached image. For cutting wood where lower tolerances are acceptable, I could utilise the full range of Z travel and for aluminium, I can install a raised bed fixture which will reduce the available travel, but stiffen the axis due to less extension. Sketches 3 and 4 are of more conventional setup with the motor mounted on the saddle. In this scenario, the amount of extension of the z plate from the lower bearing support to the tip of the spindle remains constant and will have to be rather large to achieve the desired Z travel. Does my thinking make sense, or have I missed something?

Peter, thank you for calculating and verifying my choice of stepper and screw are sufficient, and also for attaching the worksheet so I can carry out my own calculations. I think I'll use a motor with brake and only add a counterbalance if it proves to be necessary after the machine is built.

As for the Z capacity, 125-150mm should be more than enough. I will be building electric guitars not acoustic, so they should comfortably fit within that range. However, my design as it stands now has around 200mm of Z.

[mactec54]

Hi everyone,

Thank you for the feedback re Z axis support. The reason I chose a moving motor setup for the Z axis was to achieve a better compromise between large Z capacity while still having enough stiffness to cut aluminium. I got the idea from another build thread here on the forum. The idea is when the Z plate is fully extended, there will be a larger cantilever but the cantilever will be less when the z axis is raised. See sketches (1) and (2) in the attached image. For cutting wood where lower tolerances are acceptable, I could utilise the full range of Z travel and for aluminium, I can install a raised bed fixture which will reduce the available travel, but stiffen the axis due to less extension. Sketches 3 and 4 are of more conventional setup with the motor mounted on the saddle. In this scenario, the amount of extension of the z plate from the lower bearing support to the tip of the spindle remains constant and will have to be rather large to achieve the desired Z travel. Does my thinking make sense, or have I missed something?

Peter, thank you for calculating and verifying my choice of stepper and screw are sufficient, and also for attaching the worksheet so I can carry out my own calculations. I think I'll use a motor with brake and only add a counterbalance if it proves to be necessary after the machine is built.

As for the Z capacity, 125-150mm should be more than enough. I will be building electric guitars not acoustic, so they should comfortably fit within that range. However, my design as it stands now has around 200mm of Z.

1 & 2 is the best design, it can be a problem for max Z axis retraction, ( spindle Nose plus tool ) so allow for that.

[JayneV]

1 & 2 is the best design, it can be a problem for max Z axis retraction, ( spindle Nose plus tool ) so allow for that.

Hi Mactec,
My design is based on 1 & 2. I'm not sure what you mean regarding the max Z retraction problem. Are you referring to how far the tool tip will extend below the bottom of the gantry with the Z fully raised? I have attempted to compensate by mounting the spindle a little higher on the z plate. As it is shown in the attached image, the spindle nose is about 203mm above the bed with the z in the fully raised position and depending on the tool length, the available z capacity will be something less than that. I'm considering raising the base wall height by 40-50mm so the usable z capacity is closer to 200mm.

Jayne

[peteeng]

Hi Jayne - With your imaging can you turn "edges on" will make seeing the images easier. Coming along. Peter

[peteeng]

Hi All - Was watching this video on a HAAS build and its a big machine driven down the middle it seems with a yoke under the table. The bearings on the columns are 3 cars either side and are very widely spaced. Plus if you watch it seems an alien is working at HAAS. Peter

[pippin88]

If you have a 100mm thick workpiece, you probably will want to use a tool that can cut up to 100mm.

That means spindle nose needs to be able to raise to 200mm above the table / spoilboard.

With 1&2 picture, you can't get spindle nose above the bottom of the gantry, meaning you'll have to have 200mm clearance under gantry to cut a 100mm thick workpiece with a 100mm tool.

3&4 - you can raise spindle nose above gantry. Meaning you could have 105mm under gantry and cut a 100mm thick workpiece with a 100mm tool.

[peteeng]

OOPPs didn't add the link and it appears the Z axis motor is on the Z axis... - Peter
https://www.haascnc.com/machines/ver...ls/gr-510.html

[JayneV]

Hi Peter,
Are these images better? I turned visible edges on.
There is no link to the HAAS video in your second post. Sounds like an interesting video.

Hi Pippin,
I apologise for the earlier sketches (marked 1 through 4) if they were misleading. Those were drawn on my phone using a drawing app (Autodesk Sketchbook). I made the sketches to visualise the difference between the two ways of mounting the linear guide system, the images are not drawn to any kind of scale. See the attached CAD screen shots below for a better representation. Both are identical except for the spindle bracket location. In the second image, the spindle bracket is mounted to the z plate 50mm higher than in the first image. Everything else was left unchanged. The z plate is tall enough (400mm) to allow the spindle to be mounted higher so the tool can be above the bottom of the gantry when raised and still have enough travel to reach down to the bed.

[JayneV]

OOPPs didn't add the link and it appears the Z axis motor is on the Z axis... - Peter
https://www.haascnc.com/machines/ver...ls/gr-510.html

Love the video, thanks

[JayneV]

Hi everyone,
Is there much difference in quality between HIWIN brand rails and bearings and the BST Motion in-house brand? The HIWIN is about AUD$300 more than the BST for a full set for all XYZ axes according to the listed prices on their ALiExpress store so the higher price is not a deal breaker if the quality is worth it.

Jaye

[mactec54]

Hi Mactec,
My design is based on 1 & 2. I'm not sure what you mean regarding the max Z retraction problem. Are you referring to how far the tool tip will extend below the bottom of the gantry with the Z fully raised? I have attempted to compensate by mounting the spindle a little higher on the z plate. As it is shown in the attached image, the spindle nose is about 203mm above the bed with the z in the fully raised position and depending on the tool length, the available z capacity will be something less than that. I'm considering raising the base wall height by 40-50mm so the usable z capacity is closer to 200mm.

Jayne

I first used this Design over 20years ago, until recent years not may have used it, even though it is structurally better than the moving linear bearings, which most use.

That is correct, the placement of the bearings, determines the retraction of the Z axis or Spindle nose, the tool will always be below that, you can have the spindle so it can be mounted in more than one position, so you can find the best working position, you also have to allow for tramming of the Z axis / Spindle

[mactec54]

Hi everyone,
Is there much difference in quality between HIWIN brand rails and bearings and the BST Motion in-house brand? The HIWIN is about AUD$300 more than the BST for a full set for all XYZ axes according to the listed prices on their ALiExpress store so the higher price is not a deal breaker if the quality is worth it.

Jaye

There are a lot using BST Ballscrews and linear rails, and don't seem to have any problems with them, they make a quality product, just get the light preload, some of the Hiwin are just a copy and not the normal Hiwin quality so be careful if buying brand name parts

TBI Motion also have a quality Linear Rails and Ballscrews, which are at the same level as HIWIN

[JayneV]

I first used this Design over 20years ago, until recent years not may have used it, even though it is structurally better than the moving linear bearings, which most use.

That is correct, the placement of the bearings, determines the retraction of the Z axis or Spindle nose, the tool will always be below that, you can have the spindle so it can be mounted in more than one position, so you can find the best working position, you also have to allow for tramming of the Z axis / Spindle

Hi Mactec, what is a common method used to adjust the tramming? I was thinking slightly oversized holes for mounting the spindle bracket to adjust in the X-Z plane and shims between the spindle bracket and Z plate for the Y-Z direction. I'm sure there are better ways.

There are a lot using BST Ballscrews and linear rails, and don't seem to have any problems with them, they make a quality product, just get the light preload, some of the Hiwin are just a copy and not the normal Hiwin quality so be careful if buying brand name parts

TBI Motion also have a quality Linear Rails and Ballscrews, which are at the same level as HIWIN

Is there a reason to get the light preload, wouldn't a medium preload be more accurate?
The HIWIN I was referring to were the ones sold by BST Motion. They claim to be original but I have no way of knowing how to identify what is original and what is a copy. Fred at BST has been replying to messages promptly and answering all my questions. The prices seem quite reasonable for all their products so I will more than likely buy from them.

[mactec54]

Hi Mactec, what is a common method used to adjust the tramming? I was thinking slightly oversized holes for mounting the spindle bracket to adjust in the X-Z plane and shims between the spindle bracket and Z plate for the Y-Z direction. I'm sure there are better ways.




Is there a reason to get the light preload, wouldn't a medium preload be more accurate?
The HIWIN I was referring to were the ones sold by BST Motion. They claim to be original but I have no way of knowing how to identify what is original and what is a copy. Fred at BST has been replying to messages promptly and answering all my questions. The prices seem quite reasonable for all their products so I will more than likely buy from them.

All sales people are the same until you have a problem an then they are not available

Z1 is the normal Preload most use, if you have to much preload and try and mount the rails on non machined surfaces you will have binding and will wear very quickly, so if the preload is to high then you will have a problem with them, the medium may be a Z1 preload, the color of the seals are a good indication of a copy, they are not quite the same Hiwin color , so once you know what model Bearing you want go to the Hiwin site and down load there model and compare the sealing system being used it should be the same as what BST is selling

For traming it is best to have a say 19mm pin in the center of your mount, this will act as a pivot point, you can then have a grub screw each side at the top, which can push against a pin, you can also use an eccentric cam also to do this adjustment. this gets you Left to right adjustment, the forward and aft adjustment for your build is normally done at the linear Bearing each side of the gantry

[mactec54]

Love the video, thanks

That is a good example of this moving rail design, you want the Linear Bearing at the bottom of the Z Axis mount plate, if you need more clearance lift the gantry up higher, so you are working with your spindle Nose to Table clearance, don't compromise the design by moving the Linear Bearing up