[ahacking]

Hi,

I'm looking for any feedback on a steel frame fixed gantry design (below). My goal is to use this machine primarily to work with soft metal and a little bit of mild steel.
This is still in the design phase and I'm happy to modify.

Design
- Overall approx 48" long. 40"wide and 20" tall
- Working area approx 29x24"
- Table made from 1" Al, approx 29x24".
- Crossmember is 4x8" hot rolled rectangular tube (1/4" wall)
- Pillars - 4x4 hot rolled sq tube (3/8" wall)
- Base - side runners (2x4x0.120")




Specific Questions:

1) I have yet to select a spindle and would like input here - vendors, type, size etc

2) Rails - looking at HiWin made in Taiwan imported from China.
Are these overkill in size? Would 15mm do?
Gantry (x) 1000 x 20mm
Gantry (y) 1200 x 25mm
Gantry (z) 500 x 20mm

3) Ballscrews - C7 rolled imported from China.
Are these overkill in size? Would 15mm do?
Gantry (x) 20mm (1000mm)
Gantry (y) 25mm (1200mm)
Gantry (z) 20mm (500mm)

4) Steppers - Nema 23 (580 Oz). Are these big enough?
Figure the gantry with motor will weigh about 70 lbs
Figure the table will weigh about 50 lbs.

5) Would steel 1/2" be a cheaper alternative to a 1" Al table?

Many thanks!

Adam

[awerby]

Hi,

I'm looking for any feedback on a steel frame fixed gantry design (below). My goal is to use this machine primarily to work with soft metal and a little bit of mild steel.
This is still in the design phase and I'm happy to modify.

[If you build this stoutly enough it might be able to cut steel to some extent. But there are some problems with this design.]


Design
- Overall approx 48" long. 40"wide and 20" tall
- Working area approx 29x24"
- Table made from 1" Al, approx 29x24".
- Crossmember is 4x8" hot rolled rectangular tube (1/4" wall)
- Pillars - 4x4 hot rolled sq tube (3/8" wall)
- Base - side runners (2x4x0.120")




Specific Questions:

1) I have yet to select a spindle and would like input here - vendors, type, size etc

[Spindles for cutting steel are not usually sold separately from the machines they go on. But you'll want something with a large and powerful motor and a pulley cluster to trade speed for torque, which mitigates against the sort of Z axis you've drawn here, that's more suitable to a high-speed router.]

2) Rails - looking at HiWin made in Taiwan imported from China.
Are these overkill in size? Would 15mm do?
Gantry (x) 1000 x 20mm
Gantry (y) 1200 x 25mm
Gantry (z) 500 x 20mm

[The rails are fine, but the way you're mounting them isn't going to work too well. Hot-rolled steel isn't flat enough to mount rails on directly. And those supports under the table aren't nearly beefy enough to withstand the vibrations of cutting metal.]

3) Ballscrews - C7 rolled imported from China.
Are these overkill in size? Would 15mm do?
Gantry (x) 20mm (1000mm)
Gantry (y) 25mm (1200mm)
Gantry (z) 20mm (500mm)

[C7 rolled ball screws, while inexpensive, are not very accurate. You need to decide if your projects are going to require more accuracy than they will give you. C7 rolled ball screws will be off by +/- 50 microns over 300mm (about .002" per foot - see http://lin-tech.hennlich.cz/uploads/...gkeiten_54.pdf . That, of course, is when they actually meet the standard. If you're shopping from the cheapest suppliers in China they may have skimped on quality control. Here are some more considerations to mull over when thinking about ball screws: Ball-screw basics: Debunking the myths | Mechanical Drives content from Machine Design ]

4) Steppers - Nema 23 (580 Oz). Are these big enough?
Figure the gantry with motor will weigh about 70 lbs
Figure the table will weigh about 50 lbs.

[It doesn't really matter how much your bridge weighs, since it doesn't need to move - more weight is better, actually. The weight of the table will vary depending on what's loaded onto it. If you're planning on machining big hunks of metal, you'd better plan for more weight there. It's usually best to actually build your frame before worrying about the motors and drives; things can change in the course of a build, and you don't want to be stuck with components that won't work for your upgraded design. In this case, servos might be a better bet than steppers.]

5) Would steel 1/2" be a cheaper alternative to a 1" Al table?

[It would definitely be cheaper...]

Many thanks!

Adam

[You could also beef up the Z axis; that looks like a skinny little plate you're hanging the spindle on. What's the Z travel? The more you've got on a setup like this, the more leverage you have working against you. Metalworking spindles typically are quite massive quills, driven from the top with a spline, and don't travel more than 6 inches or so.]

[ahacking]

Thanks again Andrew.

I'll beef up the Z-axis.

All the best,

Adam

[handlewanker]

Hi.....as this is a fixed gantry type the uprights can be massive as they don't need to move.........add angled box ot tubular buttresses to the back and front of the uprights to resist the back and forth forces of the cutter.

To improve the design you could lower the table into the frame by building the side walls of the base highrer.....this will shorten the uprights and give you heaps more rigidity in the gantry.

Attached is a pic of my favourite fixed gantry bridge mill/router design that machines steel etc......you could glean a few design concepts from this design that is made in India.

BTW.......as spindles and motors are fairly bulky items it is imperative to design from the spindle mounting and slides and not as the spindle last or the frame will be out of proportion.
Ian.