[cady]

Hello everybody,

I'm currently planning to build my first CNC machine (strictly hobby), I'm looking to build a versatile machine for wood/plastic/aluminum and would love some input on the design and parts.
Is my first CNC so i might made some mistakes. I read a lot before doing it. Also i iterated like 4 time before this design.

I know my first mistake is on Z axis, is to high i think, i should lower it.

So the plan is as such:

• Dimension are around 1000x600x300, actual cut size will be smaller
• frame from 60x60 extrusions and 30x60
• 20x20 extrusion for table
• all machined aluminum plates are 12 mm
• Linnea guides are SBR20 with SBR20UU bearings on all axes
• Ballscrews 1605 C7 + BF12 BK12
• Direct drive Nema 23 oz 425oz 4.2A & Driver DM542A
• 2.2 kw water cooled spindle with VFD

my questions to the gods of CNC bilidng are:

• direct drive or belt driven? what kind of belt/width?
• is my design good, or do i need something else

would love input on these questions/the design in general.
My design can be found here https://a360.co/2M8tdsA


Adrian

[mcardoso]

Honestly it looks like a pretty solid design. I would stick with direct drive unless you feel a very strong need not to. Belts are fine, but add a fair bit complexity to mount and have low backlash. I prefer the PowerFlex GT2/GT3 profile (curvilinear) if I need to use a belt.

I would look at the gussets that link your rails to the vertical plates. I am missing how screws will attach to the carriages.

Your carriages are too close together on the Z axis. I would sacrifice a little travel for the extra rigidity. Going along with that, rigidity is a major issue on "router-style" machines. Keep the total height of the Z mechanism (vertical plates, Z axis, spindle, etc.) to a bare minimum. You will probably want it to cut 1/2" sheet well, rather than being weak for the rare job that needs a 4" thick piece of stock.

[wizard]

Im on my cell phone at the moment so comments below are subject to change!

1. The bearings supporting the gantry risers ( X Axis) are too close together and likely are a weak spot especially if using round rails.

2. Those riser plates appear to be on the thin side. Id like to see eith thicker or box sections.

3. The gantry beam size is hard to estimate from the pictures! The primary concern revolves around what you mean by aluminum machining and your expectations there.

4. There seems to be a general lack of gussets and joining plates. Personally i believe these are very important in any T-slot machine build. Im not a big fan of aluminum extrusions so yeah a bit biased. In any event you want your frame members rigidly joined together.

5. When you put your linear rails on the top and bottom of a gantry beam you create a few negatives. For one the gantry beam must be much higher for the same clearance thus working against stiffness. Second it is a lot more work to get the rails co planer on two different planes.

In any event some quick thoughts to consider.

[cady]

Im on my cell phone at the moment so comments below are subject to change!

1. The bearings supporting the gantry risers ( X Axis) are too close together and likely are a weak spot especially if using round rails.

2. Those riser plates appear to be on the thin side. Id like to see eith thicker or box sections.

3. The gantry beam size is hard to estimate from the pictures! The primary concern revolves around what you mean by aluminum machining and your expectations there.

4. There seems to be a general lack of gussets and joining plates. Personally i believe these are very important in any T-slot machine build. Im not a big fan of aluminum extrusions so yeah a bit biased. In any event you want your frame members rigidly joined together.

5. When you put your linear rails on the top and bottom of a gantry beam you create a few negatives. For one the gantry beam must be much higher for the same clearance thus working against stiffness. Second it is a lot more work to get the rails co planer on two different planes.

In any event some quick thoughts to consider.

Ok as i don't know exactly the terms and i don't want make any mistakes, I will just ask to be sure.

1. X axis is the long axis? The distance between all bearings is 50mm
2. I don't know which is the riser plates, i attached an image with what i believe is the riser plate. Also do you have any image as a suggestion?
3. The gantry beam is compose from one 60x60 and one 30x60 profile. I don't expect any NASA precision. I hope for 0.1mm precision. And i don't care to much for time. I won't cut aluminum so often.
4. I will have gussets and joining plates, there are some that require to drill some holes in the profiles. Also i will add some triangles to keep everything stiff. I just didn't draw them because in this way the project in cleaner.
5. To put both rails on the same plane required on 60x120 profile so the gantry beam will be at the same high. I can't find any good design for that.

Sorry again for my lack of knowledge, i try to read as much as my time permit to learn as much as i can about cnc

[wizard]

Ok as i don't know exactly the terms and i don't want make any mistakes, I will just ask to be sure.

1. X axis is the long axis? The distance between all bearings is 50mm

For many people the long axis is the X axis. I prefer on routers to think XYZ with X on the bottom, the gantry Y and spindle vertical Z. However others will disagree.

A distance or spacing of 50 mm is a bit narrow. Think about how a pole will rock vs a triangular arraingeent of two poles. What you want to minimize is the abiliity to rock on those bearings and to manage the torqued applied to them.

Now with these bearings and the spacing between them realize that there are trade offs. The greater the spacing the longer your linear rails need to be thus the larger your machine will be. Some suggest that the the spacing be as wide as the gantry beam is high and probably isnt a bad idea for round rails. Such spacing though does eat up X axis travel.

2. I don't know which is the riser plates, i attached an image with what i believe is the riser plate. Also do you have any image as a suggestion?

The risers are the side plates that hold up the gantry beam.

3. The gantry beam is compose from one 60x60 and one 30x60 profile. I don't expect any NASA precision. I hope for 0.1mm precision. And i don't care to much for time. I won't cut aluminum so often.

It should be possible to do better on a home built machine. 0.1 mm is pretty course even for wood working.

Im not a big fan of mixing extrusions in a gantry beam unless they are tied to gether with a plate upon which the linear bearings are mounted. I just see it as an assembly and maintenance nightmare. Yes it can be done but from my perspective why design a weakness into a machine if you dont have too.

4. I will have gussets and joining plates, there are some that require to drill some holes in the profiles. Also i will add some triangles to keep everything stiff. I just didn't draw them because in this way the project in cleaner.

That is good. Many forget about reinforcements or dont think that they are needed. One suggestion though is to draw them in before your design is finalized.

5. To put both rails on the same plane required on 60x120 profile so the gantry beam will be at the same high. I can't find any good design for that.

Not really. The issue here is that you loose clearance vertically due to the linear bearing hanging down along with its mounting bracket. To make up the loss vertical space the gantry beam is raised higher. It is up to you if this is a problem. Generally most people tend to minimize gantry to minimize the torque it can apply to the rest of the machine.

By the way T slotted aluminum isnt the only choice you have for a gantry beam. Steel tubing can easily handle the job and provides some advantages.

Sorry again for my lack of knowledge,

Dont be sorry! The whole idea of the forums is to try to help each other.

Just remember what you see gere is mostly opinion sometimes supportted with sound engineering.

i try to read as much as my time permit to learn as much as i can about cnc

In this forum there are a bunch of sticky threads that are well worth reading. Some dive into gantry beam design others highlight other machines aspects.

One thing i can suggest is to carefully define your expectations or what you want to achieve. This can guide you in your design decisions.

For example if the primary usage is in wood you want to make sure you can achieve the proper feed rates for wood and the cutters you will be using. There is an optimal set of parameters for every combo. You cant really say you wil just go slow and all will be well. On the flip side composites and metals may require more stiffness and slower feed rates.

Designing a machine is all about balancing competeing factors. You just need to know what is important in your case.

[ger21]

Use 1610 or 2010 ballscrews.
1605 are a poor choice for a router.

[wizard]

Hi Cady;

I'm off my cell phone on a laptop and have taken a closer look at the X axis bearings and that 50 mm spacing on your untitled 18 & 19 pictures. That close spacing of the bearing blocks is really bothering me. It really depends upon what you expect as far as machining aluminum but I just don't see that arrangement, with round rails, being as rigid as I would like for machining aluminum. Spacing that close, with the high gantry, might not be good for routing of wood.

Also I'd consider profile rails if the machining of aluminum will be a big thing.

In any event the reason I'm focused on those round rail bearings is that they generally have more clearances that other solutions and the mounts themselves are not as rigid as some other solutions. By spreading the bearings out you minimize the impact the clearances have on the gantry beam.

This can be seen graphically with a big triangle set to pivot on a point centered on its base. Bearing with a given clearance and deflection under load with allow the Apex to move further when the bearings are close to the pivot point as opposed to as far apart as possible on the base.

Now different rod and bearing sets will fit up differently so how bad the situation is Is not know ahead of time. Cheaper bearings can be rather loose. On top of all of this some bearing holding blocks do allow for preloading the bearings. Even if you get the bearings to run with zero clearance the close spacing and the long torque arm of the gantry height makes for a short life span for the bearings and rails.

[cady]

Thank you @Wizard for all the info

@Ger21 I already have the 1605 Ballscrews, i will use those to see how it work for now.

I updated my design like 10 times
It can be view here https://a360.co/2nx3Anr

I changed the gantry, and lowered the Z axis.

Now the gantry beam is compose from 2x 60x60 profiles instead of one 60x60 and one 30x60.

I think i will keep the linear bearing as they are, because i need bigger working space. If that doesn't work a new plate will be easy to make and replace the existing one.

[wizard]

Thank you @Wizard for all the info

@Ger21 I already have the 1605 Ballscrews, i will use those to see how it work for now.

They will work but you will very likely not have the feed rates and rapids that would be ideal. While it does depend a bit upon usage large machines benefit from decent rapids. Feed rate limitations have to be dealt with by spindle speed changes. This can put you into the lower power end of some spindles leaving you with the frustation of having to program many passes of shallow depth.

I updated my design like 10 times
It can be view here https://a360.co/2nx3Anr

I changed the gantry, and lowered the Z axis.

Now the gantry beam is compose from 2x 60x60 profiles instead of one 60x60 and one 30x60.

I think i will keep the linear bearing as they are, because i need bigger working space. If that doesn't work a new plate will be easy to make and replace the existing one.

If you need that working space it would pay to make the machine longer right away. If you find the spacing to be a problem you will end up loosing working space you need when you upgrade the machine.