Attempt at 5 Axis. Constructive criticism is welcome.

[dfaszer]

I've seen that 5 axis design a couple times. I'm not totally against making a 5 axis down the road, but I figured it would be a good idea to follow the wisdom of the others on this forum and start with a 3 axis. I plan on making my 3 axis with the ability to move the height of my table down by ~.5" - 1.0" increments. This would allow me to place larger items on the table and have clearance for a 4th lathe axis. If I still wanted to at a future date, I could attempt to add more axes to the gantry by moving the table down as well.

[louieatienza]

I've seen that 5 axis design a couple times. I'm not totally against making a 5 axis down the road, but I figured it would be a good idea to follow the wisdom of the others on this forum and start with a 3 axis. I plan on making my 3 axis with the ability to move the height of my table down by ~.5" - 1.0" increments. This would allow me to place larger items on the table and have clearance for a 4th lathe axis. If I still wanted to at a future date, I could attempt to add more axes to the gantry by moving the table down as well.

With creative setup you can do 4 axis indexed with 3 axis CAM...

[dfaszer]

I finally got my modeling done to where I think the frame is finished.

Attached are a couple pics. I decided to go with the 3x3x.25 box tube for the gantry and have the 4x8x.25 aluminum tube to go around it. I also switched out the plate that I had for the Z axis for a U/C channel.

For the X axis acme screw, I decided to put the screw thru the tube holding the gantry. I will cap the tube with a small plate of steel, drill a large hole in it and then mount a fanged acme nut to the plate. I plan on having a nut on both sides of the tube to help reduce the backlash. I haven't figure out how to mount the X axis motors yet tho. I figured the tubing was a good start. I also rotated the x and y axis so that the x axis has 36" of travel and the Y has 48".

I'm also having some trouble figuring out how to mount the Y and Z acme screws. Anyone have any thoughts?


Lastly, since no one responded to my questions earlier, I'll post them again.

A couple questions that I have:
How does the design look so far?
For the main steel tubes, will 1/8" wall thickness be sufficient? Will .5" aluminum for the Z be thick enough?
For the gussets and angles, is it overkill? It seems overkill to me.
For the aluminum box that I made of plate around the gantry. I have easy access to some 4"x8"x.25" aluminum box. Would it be better to replace the box made out of plate with the box tube? In order for me to make it work, I would need to reduce the gantry tube to a 3"3" tube and add a couple small shims between the bearing blocks and the inside of the 4"x8" tube.. However, I think the 4"x8" box tube would be much more sturdy than the one that I could make out of plate.
Lastly, I have it set up so that I have 4 feet of travel in the X direction and 3 feet of travel in the Y direction. In your experience, would it be better to switch the two just for being able to place a whole sheet of wood on the machine? Would there be any disadvantages of this? The only real problem that I see with this is being able to get the part of the sheet hanging off to be flat with the table surface.

I think that I'm at the point where I can order material for the frame and the Y axis of the gantry. Assuming I have the blessings of the community and nothing comes up with the questions above, I will probably order some in the next week or so.






Thanks,

[louieatienza]

I finally got my modeling done to where I think the frame is finished.

Attached are a couple pics. I decided to go with the 3x3x.25 box tube for the gantry and have the 4x8x.25 aluminum tube to go around it. I also switched out the plate that I had for the Z axis for a U/C channel.

For the X axis acme screw, I decided to put the screw thru the tube holding the gantry. I will cap the tube with a small plate of steel, drill a large hole in it and then mount a fanged acme nut to the plate. I plan on having a nut on both sides of the tube to help reduce the backlash. I haven't figure out how to mount the X axis motors yet tho. I figured the tubing was a good start. I also rotated the x and y axis so that the x axis has 36" of travel and the Y has 48".

I'm also having some trouble figuring out how to mount the Y and Z acme screws. Anyone have any thoughts?


Lastly, since no one responded to my questions earlier, I'll post them again.



I think that I'm at the point where I can order material for the frame and the Y axis of the gantry. Assuming I have the blessings of the community and nothing comes up with the questions above, I will probably order some in the next week or so.






Thanks,

You don't need two ACME nuts, you can just get one anti-backlash nut. The friction at the nut decreases efficiency, assing another nut will likely almost halve that, taxing you steppers.

Also you don't need our blessings to start!

[dfaszer]

Also you don't need our blessings to start!

I was more so worried about the .125" wall for my tubing. Whether or not it would be thick enough. I don't want to order the 60+ ft of steel to find out that the wall thickness is too thin. What do you thing about what I did for the gantry with one tube inside another?

Thanks,

[wizard]

I was more so worried about the .125" wall for my tubing. Whether or not it would be thick enough.

D. Malicky explored the thickness issue in one of the sticky threads. Given enough cross section that thickness probably won't be an issue for strength as a box beam. You may have other issues especially if you wish to drill and tap to mount rails or whatever. The problem is thin webs have a limited ability to support threads. The way around this is to design such that threading the tube isn't required. One approach is to buy rails threaded for bolts instead of rails with clearance holes.

My big concern here isn't so much the wall thickness is rather is 3 x 3" tubing big enough in cross section. I look at your design and see a very long Z axis. That means a long lever arm to act on that square beam. I'd be concerned about the ability of the beam to resist twisting.

I don't want to order the 60+ ft of steel to find out that the wall thickness is too thin.

For the most part thicker tubing will be adding more mass, this isn't a bad thing in a CNC machine. However doing so adds directly to the cost of the machine.

What do you thing about what I did for the gantry with one tube inside another?

Honestly I don't like it. Here are a few points to consider:

1. you will need to get both sides of the beam parallel to a high degree of precision.
2. your Y axis saddle ends up captured between the Y axis (Gantry) verticle supports. this leads to a machine that will be much wider than needed.
3. the wrap around beam will need to have very parallel internal surfaces to prevent binding the linear bearings. on top of that you will likely need shims.
4. access could be a bear. i much prefer something that doesn't hide important elements of the machine
5. You end up bolting your Z axis to a thin unsupported part of the wrap around section.
6. prefer easy to complicated unless you have access to a well equiped shop.

Thanks,

[louieatienza]

I'd agree that for the gantry there might be better options. I'd be inclined to use heavier steel channel and rib the back; that will give a strong structure while still allowing access for possibly fastening the rails, putting drive components in, etc.

Also, for the z bearing blocks it might be better to space them out as much as possible. Doesn't make sense to put them close together if you have the room.

If you want to get a good idea for a machine similar to your designed check out projekts57 on YouTube; one of the best DIY high rail 3 axis machines I've seen. Also check out the 5 axis CNCs at CR Onsrud's website.

Finally be realistic about what you plan to machine and how fast it can remove material. What you've designed is still stiffer than most the machines I've seen here.

[dfaszer]

check out projekts57 on YouTube

I wasn't able to find anything on youtube or google.

heavier steel channel and rib the back

What do you mean by ribbing it?

your Y axis saddle ends up captured between the Y axis (Gantry) verticle supports. this leads to a machine that will be much wider than needed.

If I'm understanding this, drop my outside verticals and place them under the top horizontal, like I have the middle vertical. This will decrease the length in the X direction by 6". How would I attach the Acme screw to the gantry if I did so?

[louieatienza]

I wasn't able to find anything on youtube or google.


What do you mean by ribbing it?


If I'm understanding this, drop my outside verticals and place them under the top horizontal, like I have the middle vertical. This will decrease the length in the X direction by 6". How would I attach the Acme screw to the gantry if I did so?

Sorry it's projektss7... Video should answer your second question.

I don't think having your z carriage within the uprights is a problem, in fact most all portal CNC are built that way. That is if your future plan is to have a relatively high z clearance. If you make your gantry rails low and make tall gantry legs then you'll need to spread the bearings on rhe gantry legs farther apart making that axis longer than it is now. So there's always tradeoffs no matter what the design.

I don't think there's a problem with your captive saddle design other than finding a tube that fits exactly. Having the screw in the back pulls the z carriage closer to the gantry beam which is good.

[dfaszer]

Just an update. I Ordered all of my metal yesterday thru my works purchasing department. It should get here next Monday.

I've been looking a lot more for linear rails and ran across this item:
1500mm SBR20 linear rail -in Linear Bearings from Industry & Business on Aliexpress.com | Alibaba Group
Could someone take a look at this item and tell me what they think? It is about $100 US cheaper than anything else I've been able to find on either Ebay or AliExpress for the same size and length and it just seems to good to be true.

Thanks,

[louieatienza]

Sure it's a great deal but without product in hand you won't know just from a pic. If can swing buying one set to see first, thst may be the safe thing to do. But with all things too good to be true, caveat emptor...

[dfaszer]

So I received my order of metal late last week and got it home. I've been able to work on it some, but with a 16 month old, there's not a whole lot of time that I can spend on my machine, so the building process will be very slow. Not that spending time with my daughter is a bad thing . I sent the plate for my gussets to a local shop with a water jet, and I should hopefully be able to get the plates back by this weekend.

I did some more searching for linear bearings and ran across a distributor on Aliexpress who quoted all of my rails and blocks for 20mm for about $350 shipped, which seems like a pretty good deal to me (if I was to buy them individually, the cheapest combination I was able to find was over $500).

On my off time, I've been trying to figure out what size ACME screw to get. I found this guide online that runs you thru some calcs, and it estimates that the minimum diameter will need to be ~.86".
Here's the link: Lead Screws: Selection Process

For the calcs, I used a gantry weight of 150-200lbs (I don't think it will weight that much, but the main beam for the gantry, 4"x6"x.18", is about 80lbs according to SolidWorks, so I was trying to play safe). The longest unsupported span is about 56". If you don't mind, could someone take a look and confirm the size of my diameter?

Here are a couple pics of my tubing:



Thanks,

[wizard]

So I received my order of metal late last week and got it home. I've been able to work on it some, but with a 16 month old, there's not a whole lot of time that I can spend on my machine, so the building process will be very slow. Not that spending time with my daughter is a bad thing .

16 months is old enough! Turn this into a farther / daughter project. . Having an assembly partner really smooths the job.

I sent the plate for my gussets to a local shop with a water jet, and I should hopefully be able to get the plates back by this weekend.

I did some more searching for linear bearings and ran across a distributor on Aliexpress who quoted all of my rails and blocks for 20mm for about $350 shipped, which seems like a pretty good deal to me (if I was to buy them individually, the cheapest combination I was able to find was over $500).

That seems to be an extremely good price.

On my off time, I've been trying to figure out what size ACME screw to get. I found this guide online that runs you thru some calcs, and it estimates that the minimum diameter will need to be ~.86".
Here's the link: Lead Screws: Selection Process

For the calcs, I used a gantry weight of 150-200lbs (I don't think it will weight that much, but the main beam for the gantry, 4"x6"x.18", is about 80lbs according to SolidWorks, so I was trying to play safe). The longest unsupported span is about 56". If you don't mind, could someone take a look and confirm the size of my diameter?

Do realize that everything else adds up pretty quick. Router, Z axis, Leadscrews and etc; all add to the weight you move around.

Here are a couple pics of my

Thanks,