Build Thread - 80/20 5X10 Woodworking CNC Build

[jsantos]

Hi All,

It's been 4 years since I built my first woodworking CNC. The first one was an 80/20 build using rack and pinion drives running on cncrouterparts bearings mounted on cold-rolled steel. Ever since I completed that first one, I've wanted to have a CNC on linear rails and running on ballscrews. To that end, I've been collecting the parts since the completion of the first one.

While the first CNC served me well, it's been acting up in the last few months. The shaft of one of the motors broke while it was routing a mahogany tea table. Luckily, it was one of the x-axis motors and the other x-axis motor was able to carry the gantry and complete the work. Otherwise, the table would have been ruined. Also, repeatability and accuracy has gone worse as the days gone by. Okay, I have not been very diligent on the maintenance aspect of the machine.

But since I've moved my woodworking workshop from my garage to my basement, it's now time for a replacement.

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[jsantos]

The new CNC will be built from the following:

1. 80/20 3030 frame. I would love to have a steel frame but I don't know how to weld, so I'll have to stick with 80/20. The size might be a problem with the 80/20 as far as sagging is concerned.

2. 35mm THK linear rails on both the x (3000mm) and y axis (1650mm).

3. 32MM (10mm pitch) ballscrew from AutomationFor Less for the x and 25mm (10mm pitch) ballscrew for the y, also from AutomationForLess. I'll have more to say about AutomationForLess' outstanding customer service later on.

4. DMM Tech 750W AC servos , drives and BOB.

The attachments are what the new machine will look like. As I mentioned earlier, my biggest concern is the possibility of sagging. I'm keeping my fingers crossed that the 35mm linear rails will stiffen the 3030 enough to minimize sagging to an acceptable level. If not, I might try to sandwich the 80/20 extrusion between the linear rail and the cold rolled steel I have from the original machine - kinda like making a torsion box.

I've been putting together the machine on Sketchup for the past month. Now it's time to start putting it together for real.

[nlancaster]

I would fear with that design your going to get alot of sag in the middle of the bed. That is a huge span. But maybe others with more experience with 80/20 could correct me. Having the CRS flat between the rail and extrusion will not do you any good. If you do ad CRS to the design to stiffen it up, attach it to the side of the 80/20 vertically. That will for sure stiffen it, I do not know if it would be enough.

[ger21]

As shown, I think you'll get a substantial amount of flex in several places.
As was already mentioned, it's going to sag a lot over the 10' span. I'd drive it from both sides and fully support the table.

I think you're two separate gantry beams are going to allow the Z axis to twist back and forth (front to back). Tying the two together into as more rigid box beam would make it much stronger.

Hanging the spindle down below the gantry beams like that will surely flex quite a bit. You're relying entirely on the stiffness of the plate which looks rather thin. If you insist on this design, I'd use at least a 1" thick plate to mount the spindle to. But, my preference would be to add something to stiffen that plate, oir get your bearings down lower.

35mm thk rails are way overkill for this design. 20-25mm rails would still be plenty strong enough, and should be a lot cheaper.

[nlancaster]

For Z-axis stiffness I would lean towards mounting the rails on the actual z-axis and the bearings for them on a plat. then the z-axis is always supported by the rails and the bearings can be fixed and further apart. may cost a bit more on having the longer rail.

[jsantos]

Thanks for the suggestions guys! Really appreciate it.

1. x-axis - I have 2 motors and drivers that I can use for the x-axis but only one ballscrew. I debated whether to drive it from both sides or just center and decided to do just the center since I only have a single ballscrew. But given your comments, it looks like the best course of action is to get another ballscrew and drive it from both sides.

2. 35mm THK rails - I was able to get the rails on eBay for very cheap over a couple of years ago, so I'm not complaining. :-)

3. gantry beams - Thanks for the suggestion. I'll change it to a plate. I've seen people use 1/2" plates. Would that be thick enough? Speaking of gantries, any thought on the extrusion uprights? Should I change those to plates too?

4. spindle plate - My z-axis is about 10" deep and the y-axis bearings are as low as I can get them and keep the 10" z. Attached is a close-up of how the z-axis is setup. The spindle is going to be attached to a 5/8" plate (spindle plate) that in turn is attached to another 5/8" plate (z-axis plate) that's attached to the z-axis linear blocks that are inside the 'green box'. The green box is a 'sealed' unit (acquired from Techno-Isel thru eBay about 4 years ago) that contains the rails and ballscrew for the z-axis. There's quite a bit of overlap between the spindle and the z-axis plate. Do you think that there will be a lot of flex on the spindle plate?

5. z axis - Also attached is a picture of the z-axis unit. There's nothing I can change here. The 2 black stripes are rubber seals that does a pretty good job of keeping the dust out of the ballscrew and rails. The black plate is the z-axis plate and is attached to the 4 mounting 'doodads' in front.


Keep comments/suggestions coming please.

[dodger889]

If you drive each side with two separate drive system and move them to the outside of the frame. Then you could add some middle supports. You asked about your gantry uprights I would do some plates for them. Now to address the gantry I would add some sorta boxing to it. that would give you a much stronger gantry then drawn.

[jsantos]

By boxing, do you mean putting a plate in front and behind the gantry extrusions?

[dodger889]

yes! or at least the back side.

[jsantos]

Just finished cutting, squaring and drilling anchor holes in the extrusions. Acquiring an old lagun cnc has been god-sent to this project. See the first 2 attachments.

Having the extrusions ready, I decided to experiment and find how exactly how much sag I will get from a 10-ft long extrusion. I mounted the extrusion about 6" from the floor, put a dial gauge underneath and hopped on the extrusion. I'm about 150lb and I figure that the gantry won't be much more than 300lbs.

The next 2 attachments show the results. The first picture is the reading before I hopped on the extrusion and the second reading was taken when I was on the extrusion. The sag is about 0.09" in the middle. The 80/20 deflection calculator gave me 0.181" on a 10-ft span, double the reading that I got! Looks like 80/20 is very conservative on their calculation.


Then, I added the rail to see if the rail would help stiffen the extrusion. The last 2 attachments show the result. The sag is now about 0.07". The rail stiffened the extrusion but not enough. I might try to add the CRS later on and see how much that helps.

Based on the 80/20 deflection calculator, adding another leg in the center will reduce the sag to 0.021" sag. Adding a 4th leg will reduce it to a negligible 0.006".

Since driving the x on both sides will give me more flexibility in controlling the sag, I'm going with this option.

[jsantos]

Spent most of the day redesigning the CNC. The attached is the partially finished design.

I boxed in the gantry and will replace the uprights with 1" plates.

But driving the x on the sides will present another problem. It will leave the rails and ballscrews exposed to sawdust. Given what I've seen with my first cnc, those sawdust really like to go over the side. Anybody have any thoughts on how the rails and ballscrew can be protected from them sawdusts?

If I can't find a solution, I think I might go 5X5 instead of a 5X10. It's quite a change but looking back now, I've only cut 3 full sheets of 4X8 in the four years I had my first CNC.

Can you cut a linear rail with a cutoff saw? Will the heat generated affect the rail?

[dodger889]

If you cut them it would only effect about an inch at most. So you just cut let them cool then cut again repeat until you are all the way through. Then you will not see any damage at all.
For protecting the ball screws just add a shield to keep most of the dust from falling on them. And a dust brush to keep them clear could help too.

[jsantos]

Happy New Year, All!


Based on the feedback from some people, I did a redesign. I decided to go 5X5 instead of the original 5X10. I convinced myself that I really did not need a 5X10 as I have not been doing a lot of sheet goods work anyway.

Based on people's suggestions, here are the changes I made:

1. Shorten the X from 10' to 5'.

2. I will go with 3060 instead of 3030 to stiffen the X some more. Based on 80/20's deflection calculator, this will give me a sag in the middle of 0.001" (supported two ends) or 0.0002" (fixed two ends). Don't really quite understand the difference between the two. If the worst case is 0.001", I can live with that. Besides, based on my experiments with deflection, I think that the deflection calculator is conservative.

3. As Gerry and Dodger suggested, I boxed in the gantry to stiffen it up. It will be interesting to see if I can accurately drill and tap the holes in these plates.

4. As Dodger suggested, I changed the uprights from 3030 extrusions to 1" plates. The shape of the uprights was dictated by where I calculated the center of gravity was going to be. I didn't think I was going to be over 300 lbs on the gantry but based on weighing and calculations, it's going to be a 400lb gantry.

The gantry still looks too tall. I cannot bring the lower rail lower but I can lower the upper rail. Should I do that? How close can the rails be? Given that my Z-axis is very tall, does that impact how far apart my y-axis rails can be?

Although Gerry suggested that I go with 1" plate on the spindle plate, I will go with the 5/8" since I already have that. I can easily replace that later on if I need to.


Thanks for the suggestions on how I can improve this machine. Any other suggestions before I go gung-ho on building this?

[jsantos]

Have been noodling with the design and have made more changes:
1. I lowered the gantry by a foot so it doesn't look so tall now. Reduced weight and cost too. :-)

2. I was shopping around for aluminum for the uprights and found some 1 3/8" that I was able to get cheaper
than I would have paid for a 1" so I will be using a much thicker upright.

The first attachment shows the redesigned gantry.

The second attachment is the completed frame. To make it easier to mount the rails, this was assembled
upside down. I then had a friend help me turn it right side up.

The last attachment are some parts for the x-axis. I milled channels in them to make aligning the parts easier -
easily the smartest decision I've made on this project. :-)

[jsantos]

Finally completed the x-axis. I can rotate the ballscrew shaft with my hand and move the linear rails very smoothly from end to end with no binding at all.

I'm surprised at how well everything is fitting together. So far, all the parts have fit perfectly. I relied entirely on Sketchup Pro for all my dimensions and it seems to have done an excellent job. Now if someone will only come up with a CAM that works with Sketchup Pro. :-)

I've also started laying out the electronics. I'm going with DMM Tech's AC Servos, DYN3 drivers and their BOB. It looks like I'll end up with a panel that's about 2' X 3'. This is a lot bigger than I expected! Oh, well. Based on my calculations, I should be able to get like 750 ipm out of servos. Don't know if the other mechanicals will be able to handle that much speed. I'll soon find out.

[tahustvedt]

The table is looking great, but I think you will need two ball screws to avoid racking since the X bearings are so close together.

Are you planning to support the bottom of the X axis stepper/ball screw plate? It will flex if it's not supported.

[widgitmaster]

The table is looking great, but I think you will need two ball screws to avoid racking since the X bearings are so close together.

Are you planning to support the bottom of the X axis stepper/ball screw plate? It will flex if it's not supported.

I agree with tahustvedt, when the screw pushes against the gantry, there is nothing to counter the force! You need to add triangle gusset's on each end plate!
Widgit

[jsantos]

Hadn't planned on putting supports at the bottom of the end plates but now I will. I have to remachine the plate with the motor to make my idler wheel adjustment hole bigger so I will add holes to make provisions for adding support at the bottom. The timing of your comments are perfect. :-)

I had not originally planned on using two ballscrews to drive the x- but it's been in the back of my mind. I've been researching how to drive two screws with a single servo in case I'm forced to do that.

[jsantos]

Been busy machining the gantry uprights and the front and back plates. It's been an experience learning how to machine parts that are larger than your table.

I'm using Vectric's Aspire to machine my parts and since Aspire has the tiling option, I thought that I would use that to machine the parts. I first did the uprights. Although Aspire's tiling option have quirks, it worked. I do have a concern that the top and bottom might be a little off because there is a ridge on the side where the first tile machined and the second time machined met. I'll find out if it's a problem when I add the horizontals.

While Aspire's tiling option seems to have worked on the uprights, I did run into all sorts of issues when I worked on the plates. The plates are 1700mm long and my table is 600mm on the x-axis.

The first problem with Aspire's tiling option came when I tried a toolpath to trim the edges of the plates. If I don't have the tiling option on, Aspire happily shows me how it will trim the edges. Once I turned the tiling option on, Aspire doesn't do anything. It gives me an error saying it couldn't save the toolpath. I emailed Vectric support and all I got from them was that my toolpath was outside my tiles, no other explanation. After I mentioned on the Vectric forum that I wasn't getting an explanation from Vectric support on what's happening, Brian of Vectric finally explained it. But it looks like I POed them off. Other emails about other issues I'm having with the tiling option have since gone unanswered.

Because the toolpath that's being generated by Aspire looked weird, I decided to do some experiments before I started machining the gantry plates. Here's what I found out. Some of these issues may be because I don't know what I'm doing, so take these with a grain of salt.

1. The drilling toolpath also retracts to the safe Z instead of retracing to the retract gap. Since my safe Z was 2 inches high because of my clamps, it was taking a long time to drill. Since I had a lot of holes to drill, that was a problem. This was the last issue that I sent to Vectric support. And like I said, I never got a response back from them.

2. I turned ramping on my pocketing toolpath and Aspire happily did ramping on the first tile. It forgot all about rampng on the other tiles.

3. With the tiling option off, Aspire would rapid down from the safe Z to the plunge Z. Then it would come down on the material on the specified feed rate. With the tiling option off, Aspire would come down on the material at the specified feed rate immediately! This makes for a very long machining! Oddly, it seems to only do this on the first plunge.

4. Aspire pockets the first tile perfectly but does not completely pocket the other tiles, leaving ridges in the pocket.

While I am a fan of Aspire, I thought that the tiling option is not ready for prime time. As I did not want to ruin my plates, I decided to do the tiling manually.

Now, I'm ready to machine the plates. This is where more learning experience came in!

[jsantos]

More of my learning on machining...

I was going to machine a channel on the front plate for the rails to sit on. The machining of the first tile went great. But when I machined the second tile, the depth of the pocket was not the same as the first tile! Nooooo! So I tried the 3rd tile. The same thing! I had the plate sitting on stand-offs because I was also drilling. I thought that I might be having problems with the pocketing because the plate was not sitting flat on the stand-offs or the stand-offs were not even. I finished the drilling and then took the plate off the stand-offs and set it on the tooling plate. My tooling plate is supposed to be flat to 0.003".

I tried the first tile and then the second tile. The same problem - the pockets for the first tile was not the same depth as the first tile! What's going on! Then I noticed that the plate was not sitting perfectly flat on the tooling plate! Oh! I removed the plate and saw that there were some chips on the plate. Argg!. Cleaned up the chips and make sure the plate is sitting flat. No, it wasn't! Double Arrgggg!

The gantry plate is against 2 locator pins on the side and another index pin in the center. I also drilled another hole in the center for my clamp. I was only using a single clamp on the center to hold the gantry plate down. Now I put 2 clamps each on each side where each tile ends. This time, it looks like the gantry plate is sitting flat. Try again. Success! While I can see where the first tile ends and the second tile begins because of the tool swirl marks, I cannot feel any ridge.! Anyway, I was going to have a 2mm channel that ended up as a 3mm channel but I'm happy with the result. Lesson learned.

Finished products shown in pictures below.

I will talk about my rail cutting experience in the next post.