[janz99]

Has anyone ever used some of the cheaper linear guide rail/ball screw packages they offer on ebay? There is a few kits with varying lengths that are very reasonably priced. It says its a C7 grade so they are definitely a low end rail, but for a DIY home cnc router I was wondering how well they might work. I really like the idea of using a nice linear rail and ball screw setup, but for a small hobbyist/home built router, I just cant justify spending 800-1000$ + on a set of good rails/ball-screws.

If these are deemed no good, is there any vendors on here that sell a reasonably priced set of rails? I am looking to make a router for cutting alum, and light steel in a 24"x36" machine size range.

I'm not sure if linking ebay pages is allowed on this forum, so please remove if this is a violation of forum rules. Here is the kit I was looking at:

SBR20 Linear Rail Set 3 ballscrew RM2005 350 850 1150mm BK BF15 Bearing CNC Set | eBay


Thanks
Ryan

[hanermo]

The SBR rails are useless for cutting alu.
You need profile rails.

For cutting steel you need a machine about 10-50x more rigid than for alu == wood.

A 24x36 cuttng area in steel, needs a machine about 1000 kg in mass in steel or cast iron.
If using a bridge mill or moving table.
For gantry, much more mass, much bigger section size.

Fyi..
A built a machine for milling steel, with a moving table of even bigger size.
35 mm size linear rails, 32 mm ballscrews.
2000 kg in mass in steel.

[janz99]

I'm not looking to machine heavy/thick steel. Possibly some 1/4" plate that I can cut some 2D parts out of, or face off a small block of steel, taking light cuts. For the most part, it will be cutting alum. for brackets or small automotive projects that come up on our race car. I'm just looking to build something that will give me some CNC capability but not break the bank as far as buying a cnc mill or Bridgeport mill with cnc conversion. I was hoping to keep the cost of this machine down under the 3-4000$ mark including a bit of tooling ie -vice, holders, etc. I've seen a few videos of users cutting steel on their router tables, and figured it should be more then do-able as long as time isnt a factor.

If the consensus is that this is asking way to much out of a machine like this, then I guess I will have to revisit my current situation, and try and come up with another solution. Originally, I had planned on buying a small desktop harbor freight style mill and converting it to cnc, but the table and workable area is just a little to small for most car projects I have in mind for it. This is why the idea of using a cnc router with steel frame construction came to mind. I figured it may not be the best option, but it would have the most versatility as far as machining options would go.

[ger21]

Cutting any steel is like night and day compared to cutting aluminum.
I've seen a few people cutting steel on a router, but their only removing a few thousandths at a time. You also need to consider coolant, and spindle speed.

As was mentioned, the round linear shafts are just not very good. They have some play and them, and they really aren't that good for a wood cutting router.

You can get chinese profile rails for not much more, or higher quality Hiwins for a bit more than that. Check BST Automation on Aliexpress for the best Hiwin pricing.

[janz99]

If its just the actual rail design you guys are concerned about, I will have a look at an alternative to the round supported style. I looked at some used THK SHS25 rails and trucks, but it was $700 for a used set. That's a bit more then I would really like to spend for 2 sets of rails. By the time I had all the rails and ball screws id be into just the linear motion for $1500+ and that doesn't include the cost of stepper motors.

Ideally id be looking to take .015-.02" depth of cuts with a 3/8" carbide endmill. 30-40ipm in steel would be fantastic at those depths of cuts. Is this realistic for a machine like this or am I asking for trouble. Maybe I should be looking at converting a small desktop mill, and dealing with the size constraints by getting creative with setups.

PS- I just had a look at the hiwin rails, and it looks like those could definitely be an option. They are slightly more expensive, but if they will hold up to what id like to do with this machine, then I can justify the added cost.

[awerby]

You can probably find better deals on linear profile rails, but spending $1500 on the linear motion part of your project sounds pretty realistic. If you want to cut steel, that's the least of your worries. The DOC and speeds you mention would be feasible on a full-sized commercial knee mill when cutting steel, but on a home-made router-type machine with round rails they do indeed sound fantastic.

Putting together a frame that's heavy-duty enough should be high on the list. There's a reason why milling machines intended for steel look the way they do; it takes a very substantial machine to make much impression on the stuff. 24" x 36" is small for a router but large for a mill; most of them, even big ones, have a much smaller Y axis. Here's a current thread by someone who is making his own frame for a machine that's intended for steel; he has some idea of what he's up against, and is calling it a light-duty machine: http://www.cnczone.com/forums/vertic...g-machine.html

Most people who want a machine like that start out with a frame from an older cast-iron mill and retrofit it. Just because you only have a certain amount of money to spend doesn't mean that the machine you build with it will somehow rise to the occasion and do everything you want it to. Even if price is no object, the very expensive machine you build might not perform to expectations, but if you set an arbitrary limit to the amount you'll spend on some particular part of your project, the chance of that happening increases substantially.

[ger21]

What do you plan to build this machine from? Do you have a design in mind?

Ideally id be looking to take .015-.02" depth of cuts with a 3/8" carbide endmill. 30-40ipm in steel would be fantastic at those depths of cuts. Is this realistic

No, not realistic at all.

[janz99]

I haven't started any hard designs yet, but I do have a few ideas kicking around. I was thinking of using 2x3x.187/.250 wall for the framing. I'm not quite sure about the gantry yet, but after posting this I'm having second thoughts about if this machine will be up to the task. I don't do a ton of steel machining, mostly alum parts for my race car, but on occasion I machine stainless flanges or steel flanges.

I might be better off starting out with a grizzly bench top mill or the little machine shop mill and converting it to cnc. It doesn't give me the working area I would ideally need, but I might be able to get creative with multiple setups. I don't have a huge budget for this, and I'm not sure the budget is large enough to get what I want/need out of a machine like this.

[jfong]

I haven't started any hard designs yet, but I do have a few ideas kicking around. I was thinking of using 2x3x.187/.250 wall for the framing. I'm not quite sure about the gantry yet, but after posting this I'm having second thoughts about if this machine will be up to the task. I don't do a ton of steel machining, mostly alum parts for my race car, but on occasion I machine stainless flanges or steel flanges.

I might be better off starting out with a grizzly bench top mill or the little machine shop mill and converting it to cnc. It doesn't give me the working area I would ideally need, but I might be able to get creative with multiple setups. I don't have a huge budget for this, and I'm not sure the budget is large enough to get what I want/need out of a machine like this.

I bought a X3 bench mill and converted it to CNC. Used that to machine the aluminum parts for my 80/20 extrusion gantry CNC. Total was around 4k for both but I bought all the THK linear rails, servos, steppers, extrusion and gecko201/320 drivers off eBay for very cheap. I would get a G0704 mill now but it wasn't available back then. I use the x3 to machine all the aluminum and steel parts for my hobbies and the gantry for my woodshop. The occasional aluminum plate on the gantry if it is too big to fit on the mill. I would never attempt to cut steel on the gantry but I suppose it can since I've ran into socket cap screws that I use for hold downs by accident. Seems to cut them just fine.

[janz99]

I bought a X3 bench mill and converted it to CNC. Used that to machine the aluminum parts for my 80/20 extrusion gantry CNC. Total was around 4k for both but I bought all the THK linear rails, servos, steppers, extrusion and gecko201/320 drivers off eBay for very cheap. I would get a G0704 mill now but it wasn't available back then. I use the x3 to machine all the aluminum and steel parts for my hobbies and the gantry for my woodshop. The occasional aluminum plate on the gantry if it is too big to fit on the mill. I would never attempt to cut steel on the gantry but I suppose it can since I've ran into socket cap screws that I use for hold downs by accident. Seems to cut them just fine.

That could also be a great option that I had never considered. Again the only downside to the bench tops is their limited machining window. Thanks for all the suggestions, I have book marked the Hiwin rails, and will start looking at a few of the heavy duty router designs. I still don't want to give up on the idea of using only a router to do some light steel machining, It just may require a larger budget and a more ridged base/gantry then I was originally planning.

https://youtu.be/Z-_z0n1nRdk

This guy seems to be cutting steel on his router, to bad you can't see the entire machine to get an idea as to how ridged it really is.

[alan_3301]

It's right here if you want to read about it

http://www.cnczone.com/forums/cnc-wo...minum-cnc.html

[janz99]

That router looks and functions very well. It gives me some confidence that I can actually make a router work the way I think it could, without breaking the bank.

[awerby]

That's an exceptionally rigid gantry router, but he never said it was up to milling steel. If you do a really good job, you can build a machine that's able to cut aluminum like his can.

[janz99]

I wonder if his gantry was made from steel if it would add to the ridgidity of it. I know it would be a lot heavier, but I'm not looking to cut material at 300ipm. Anything around 80-100ipm in alum would be amazing and rapids in the 200ipm range.

It would probably require some larger steppers, or possibly dual steppers in the x to move the gantry at those speeds. What do you guys think?

[awerby]

To maximize rigidity, a fixed bridge/moving table design is better than one with a moving gantry. That way, the bridge can be as heavy as need be, and steel isn't a problem.

Dual steppers are better than a single one because they avoid the "stuck drawer" effect, where the axis racks slightly and either loses squareness or jams. But bigger stepper motors don't necessarily go faster; they tend to be slower, especially when changing directions. If high speeds are what you're shooting for, consider going with servos, which don't suffer a loss of torque when turning faster.

[janz99]

Im not looking for crazy high speeds. 80-100ipm feed rates, and possibly double that for rapids. Not overly concerned about the rapid rates, its more of a nice to have then a need to have. This will not be a production machine, just a garage/hobby machine to make some car parts and some odds and ends around the house.

Whats the largest stepper you can go with and still achieve speeds in this area? I think if I can make a moving gantry, but still have it out of steel, it would keep things fairly ridged.

[ger21]

200ipm rapids will seem painfully slow in a very short time.

What pitch ballscrews do you plan on using?

[janz99]

I haven't thought about that yet. I'm still in the design phase for the framing.

[ger21]

Your choice of stepper would depend on your choice of screw.

[janz99]

I'll probably need to know the weight of the gantry assembly before I can defied on a stepper, correct?