[nummi]

I’ve been reading this great forum for over a year now and planning a router for a while. I’m going to use it mainly for wood, but it would be nice to be able to cut aluminum.

Working area about 1100x800x140 mm. Frame is mainly steel because of strength and low price. Y-axis car and Z-axis are made of aluminum.

My budget is very limited, but I got rails and ball screws at good price. I’m planning to make strong enough frame. Other parts can be updated later if needed, such as controller, router, motors and drivers.

At first I’m going to use Bosch POF 1200 AE router, Arduino GRBL as controller

The frame is bolted together, no welds. Mostly 5 mm thick wall, but some parts that doesn’t need threading are 3 or 4 mm. I’m going to use epoxy to level base for rails and also use it to flat all connecting surfaces before bolting. For Z-axis rails base I have aluminum bars, shown in pictures.

Parts that I already have:
Rails are 20 mm THK profile rails for all axis.
Two identical 2010 ball screws, lenght 1200 mm for x-axis.
One about 200 mm 1605 ball screw.
Four Wantai Nema 23 425oz.in, 3.8mH.
Four PiBot stepper drivers PiBot Stepper Motor Driver Rev2.2 (Compatible Many Boards Output 4.5A)
Two power supplies 40-60 V, 25 A.
Cabinet for electronics.
Some parts of aluminum and steel tubes.
Bosch POF 1200 AE router.

I have only some basic tools to work with:
Small drill press, miter saw, angle grinder and track saw. Maybe access to lathe.

In pictures the gantry is 200x100x6 mm. Will it be strong enough compared to rest of the design?
How high and low should the router be able to move with regular bits?
Any thoughts about the design?

[nummi]

Some parts that I have.

[wizard]

At first blush it looks like a well thought out machine.

From the drawings I don't fully grasp how the uprights for the gantry support are made. If you will be buying lots of tubing I would come up with a tubing solution.

Also while I understand the desire to avoid any welded parts, too reduce distortion issues, sometimes a welded fabrication can be a huge win in a design. For example the rungs or your table top support members could have their angle iron brackets welded on to simplify assembly. At the ends of the tubes any distortion of the tube will be minor. The only real trick from a welding standpoint is to get the angle iron brackets square to the tube and make each rung exactly the same length. The same thing might be suggested for the gantry beam uprights though they would get into machining requirements.

With a bolted together structure it is sometimes advisable to make use of through bolting and this means making things accessible to put nuts on or to apply a wrench. I would want to see fairly hefty bolts for some of the structural connections. For the bolts the web of the steel sections would be too thin to bother tapping. We are talking bolts in the 3/8" to half inch range. The idea here is to have plenty of clamping force available out of the bolts to make sure the bolted joint ends up with metal to metal contact.

This issue with being able to get to the bolts is often simplified with Allen Head Cap Screws. As you can drill small holes in the opposite sides to access the cap screw with a skinny Allen wrench. A ratchet ( fine toothed) and socket often are needed for the nuts. Finally you can't bolt what you can't reach. With your design I don't see a huge problem with reach, the critical joints are easy to reach in most cases.

You seemed to have forgotten diagonal bracing at the ends. This is important and X bracing at each end is advised. Your diagonal bracing doesn't have to be extremely heavy to do the job and can be bolted in place by drilled and tapped holes. This applies to all diagonals, I'm not sure the fat diagonal beams on your Z axis adds enough to be worth the cost. You need the bracing of course but cheaper members may do well enough. I need to think on the X axis diagonals a bit, you already have designed in because the layout looks to be pretty smart. There is more than one way to do this obviously. Finally I'm not seeing any X bracing for longitudinal movement of the two X axis frames. You can't rely upon the rungs in a bolted up machine to resist such movement.

I know I spent a lot of time on diagonal bracing but I believe it is critical in a bolted up machine. Even in a welded up machine it can make a significant difference.

Finally for all your joints consider dowel or roll pinning everything in place once the machine is assembled and everything checks out to spec.

[nummi]

Thanks for good answer wizard.

At first blush it looks like a well thought out machine.

From the drawings I don't fully grasp how the uprights for the gantry support are made. If you will be buying lots of tubing I would come up with a tubing solution.

Here is some pictures of the structure. This way I think it could be bolted together pretty easily. I already have the aluminum plate.

Also while I understand the desire to avoid any welded parts, too reduce distortion issues, sometimes a welded fabrication can be a huge win in a design. For example the rungs or your table top support members could have their angle iron brackets welded on to simplify assembly. At the ends of the tubes any distortion of the tube will be minor. The only real trick from a welding standpoint is to get the angle iron brackets square to the tube and make each rung exactly the same length. The same thing might be suggested for the gantry beam uprights though they would get into machining requirements.

Good point about welding the angle irons. As I'm going to use epoxy or polyester filler in every joint to make surfaces flat, I don't think small differences in lengths will be a problem.

With a bolted together structure it is sometimes advisable to make use of through bolting and this means making things accessible to put nuts on or to apply a wrench. I would want to see fairly hefty bolts for some of the structural connections. For the bolts the web of the steel sections would be too thin to bother tapping. We are talking bolts in the 3/8" to half inch range. The idea here is to have plenty of clamping force available out of the bolts to make sure the bolted joint ends up with metal to metal contact.

This issue with being able to get to the bolts is often simplified with Allen Head Cap Screws. As you can drill small holes in the opposite sides to access the cap screw with a skinny Allen wrench. A ratchet ( fine toothed) and socket often are needed for the nuts. Finally you can't bolt what you can't reach. With your design I don't see a huge problem with reach, the critical joints are easy to reach in most cases.

I was planning to use Allen Head Cap Screws. Through bolting is definitely smart when it's possible.

You seemed to have forgotten diagonal bracing at the ends. This is important and X bracing at each end is advised. Your diagonal bracing doesn't have to be extremely heavy to do the job and can be bolted in place by drilled and tapped holes. This applies to all diagonals, I'm not sure the fat diagonal beams on your Z axis adds enough to be worth the cost. You need the bracing of course but cheaper members may do well enough. I need to think on the X axis diagonals a bit, you already have designed in because the layout looks to be pretty smart. There is more than one way to do this obviously. Finally I'm not seeing any X bracing for longitudinal movement of the two X axis frames. You can't rely upon the rungs in a bolted up machine to resist such movement.

Diagonal bracing definitely is insufficient and now I added some. X axis diagonals and many others parts of the structure was copied from this machine http://www.cnczone.com/forums/cnc-wo...ilt-steel.html

Z axis diagonals are 15 mm thick and I have material for that.

Finally for all your joints consider dowel or roll pinning everything in place once the machine is assembled and everything checks out to spec.

That is my plan. Already bought some dowel pins. Not sure how accurate drilling I can do with hand drill.

[wizard]

Thanks for good answer wizard.



Here is some pictures of the structure. This way I think it could be bolted together pretty easily. I already have the aluminum plate.

Aluminum plate with steel structural tubing isn't ideal. It will work as long as there is no vast temperature increases on parts resulting in differential thermal expansion.

Good point about welding the angle irons. As I'm going to use epoxy or polyester filler in every joint to make surfaces flat, I don't think small differences in lengths will be a problem.

For the table support rungs you should be able to weld them accurately enough not to require messy epoxy which would be a pain on vertical surfaces. You would need to make up a fixture of some sort to get repeatability to a decent place. The fixture could be built upon one of your tubular sections before it is used to brace the machine or whatever.

I was planning to use Allen Head Cap Screws. Through bolting is definitely smart when it's possible.

Obviously it isn't needed everywhere. Where it is needed though you will want to find a way.

Diagonal bracing definitely is insufficient and now I added some. X axis diagonals and many others parts of the structure was copied from this machine http://www.cnczone.com/forums/cnc-wo...ilt-steel.html

I will have to look into that.

Z axis diagonals are 15 mm thick and I have material for that.



That is my plan. Already bought some dowel pins. Not sure how accurate drilling I can do with hand drill.

The accuracy with a drill will be plenty good. You simply want to be able to place the pins to keep alignment if something should happen to loosen over time you will need a reamer though as dowel pins require fairly tight tolerances on the hole diameter. Roll pins are somewhat more flexible.

I really like what you got so far! I'd consider walking through the assembly process, in your mind, a couple (several) of times. With assemblies like this finding the optimal assembly sequence isn't often obvious. This might reveal to you problems we haven't seen yet. A bolted together machine assembly can be likened yo the challenges a machinist has making a part. It is completely possible to get half way through a matching job and suddenly realize that you should have machined a feature earlier in the process and now you are stuck coming up with a way to do that feature.

[nummi]

The frame is almost finished. I changed the design a bit to fit tubes I found from a junkyard and to be able to use as much through bolting as possible.

The bolts are 8 mm and 10 mm. First side hole was drilled to bolt size and opposing hole 1 mm oversize to enable alignment. My column drill was so weak, that I had to drill all holes larger than 6 mm with hand drill.

Plan was to use epoxy between connecting faces, but I haven't decided in what order I should assemble the frame to do that. Maybe I make only some of connections dismountable and rest of the connections will be glued permanently.

[wizard]

Looking good!

[nummi]

Some older pictures.

I did all cuts with angle grinder and guide.

[nummi]

When all part was lined up I disassembled everything and painted the parts.

[nummi]

Then I assembled everything again. Next I removed one peace at a time and added epoxy to joints.

Parts along the x-axis are glued and parts along the y-axis can be taken apart.

[nummi]

Frame is almost finished. Some tread lock has to be added to bolts and drill holes for dowel pins. What size hole should I drill for 5 mm spring dowel pins before reaming?

This way of building has been very slow and if I would do it again, I would make a jig, glue pieces together and then drill holes and bolt.

[wizard]

Nummi,

Looking good! Looking forward to seeing this machine produce.

This thread highlights in my mind the value in considering steel. If one takes the time to look, steel can be had amazingly cheap.

[fretman_2]

It's built like a brick shirthouse!

[nummi]

This thread highlights in my mind the value in considering steel. If one takes the time to look, steel can be had amazingly cheap.

Did some calculation how much have I spent so far:

Steel, 160 kg 80 € (bought about 180 kg, 160 kg was used)
Aluminum 10€
Bolts, nuts, washers ~30€ (118 pcs M8, 24 pcs M10)
Paint 47€ (3x750 ml)
Brushes 10€
Brake cleaner 6€
Epoxy 5€
Thread lock 14€
Cutting disks 20€

Total: 222€

Steel was actually quite cheap. Now when I look at it I could have bought a bit heavier tubes with only small increase in total price.

[qbvbsite]

That looks awesome . I'm thinking of using steel as well, can you list the size of bars you used at each section? I have never welded before that's why i'l looking to bolt everything together

--James

[nummi]

Here are some measurements based on memory.