Steel Gantry Machine 1500x750x200

**Richard** · 15-01-2018

Very nice build! Is this really your first one??? Can I ask a couple of questions?

Did you use epoxy on the gantry as well or did you get it machined flat?

Did you have any problems getting everything square?

I see you have the z rails on the moving z plate, which is the better method. Is the z plate rigid enough with just the rails bolted to it? I wondered if C channel steel or a box made from ali plate would be better? (the rest of the machine looks super rigid)

(that's 3 questions! Sorry!)

**toomast** · 15-01-2018

Originally Posted by Richard

Very nice build! Is this really your first one??? Can I ask a couple of questions?

Did you use epoxy on the gantry as well or did you get it machined flat?

Did you have any problems getting everything square?

I see you have the z rails on the moving z plate, which is the better method. Is the z plate rigid enough with just the rails bolted to it? I wondered if C channel steel or a box made from ali plate would be better? (the rest of the machine looks super rigid)

(that's 3 questions! Sorry!)

1. Yes, its my first CNC machine build.
2. I used epoxy on the gantry too.
3. Squareing is time consuming. Have to use creativity and long machinist squares.
4. I can measure quite a lot of deflection on my Z. For sure you can design it stronger. Steel is more rigid. It all depends on your requirements and budget. It is nice to have a super strong machine, but it all comes with a cost. Also I like to point out that good machinist can produce superb parts with mediocre machine. There is no black and white, only gray :D

**Richard** · 15-01-2018

There is no black and white, only gray :D

Ha! very true!

Your design is very similar to one I started to draw up, with the deep sides to avoid the bendy gantry sides many people have...

I wanted to as long Z travel as possible, so I used steel channel for the Z plate. The fusion360 sim showed that a flat plate would flex a lot.

Your build is very impressive and it looks really nicely finished.

Do you make any mistakes at all???

Would have done anything differently?

So how did you do the epoxy on the gantry? I can see you have rails on the top and underside of the gantry (good design to keep Z close to the gantry!), so the top epoxy would be easy! The bottom????

**routercnc** · 16-01-2018

Hi Toomast,

In support of post #84 (but not an answer !) I also use F360 for CAM and Mach3 for control. I had a similar problem, although the other way around.

One of the last parts I cut out (a simple rectangle) was roughed out with 0.1 mm stock to leave, then a finish pass was applied. I forgot to do the finish pass on one of the parts (and had removed it from the machine) but as the dimension was not critical I left it there. One the second part I made sure it did the rough and the finish.

When I measured them both the first part was spot on the dimension (but should have been 0.1 mm larger) and the second part was 0.1 mm underside (but should have been OK). As they were simple cover plate it did not matter but I wondered what had happened.

I've cut lots of part out and not seen that before. Unfortunately my machine is now a pile of bits so I won't find out any time soon. Just thought I'd post my experiences . . . .

**toomast** · 16-01-2018

Hi routercnc,

Thanks for shareing. Las night I did some experiments. But now I realize I only did contour cuts. I tried all compensation options but results where the same. Inside dimension spot on and outside 0,3mm extra.

Does Mach3 DRO shows coordinates with compensation or without? Since DRO (both work and machine) was spot on but cut was 0,3mm off... Right now I already doubt my axis calibration. Workshop is a bit colder but i dont think shrinking is to blame here.

**needleworks** · 16-01-2018

If you are using an adaptive toolpath in fusion, are you also following it with a 2d contour ? In fusion when you use 2d adaptive, there will be an option for "radial/axial stock to leave" You can of course set these to 0, but I always follow adaptive toolpaths with a 2d cleanup contour.
Just a thought !

**toomast** · 16-01-2018

Originally Posted by needleworks

If you are using an adaptive toolpath in fusion, are you also following it with a 2d contour ? In fusion when you use 2d adaptive, there will be an option for "radial/axial stock to leave" You can of course set these to 0, but I always follow adaptive toolpaths with a 2d cleanup contour.
Just a thought !

Yes. In 2d adaptive I leave 0,5mm stock. Which I clean up with 2d contour as a finishing pass.

**Davek0974** · 16-01-2018

Originally Posted by Neale

What cutter are you using, and how accurate do you believe it is?

I normally use single-flute cutters, and my experience is that they tend to cut as if they are slightly smaller than their marked size. For example, I get pretty accurate results from my nominal 6mm cutter if I specify it as 5.7mm in my CAM software.

I spent a lot of time chasing this kind of inaccuracy and whatever tests I did, the machine seemed to be pretty good. However, when I cut a simple test square and measured it, the size was always wrong. Now, I do a quick test with every new cutter to work out its "real" diameter. The problem is that you cannot just measure single-flute cutters. Maybe they are just cheap cutters and no-one else seems to have this problem, but this is the only way I can get accurate, consistent, results.

Looking again at your measurements, though, I'm not sure that this is the case here. If, for example, the cutter were cutting 0.3mm undersize, the internal dimension would also be wrong (29.7mm). Similarly, a scaling error would also see errors in the internal dimension. Maybe it's something silly like using an offset in the CAM settings for the external cut? Or did you forget the finishing cut? Sorry if this sounds rude, but sometimes the answer is a small error that you have made and you only find it when you show it in public! That is something that you might find if you examine the gcode.

I think its normal - I do exactly the same with all my cutters, the 2mm SF carbides i use only give true results if cam'med for 1.96mm so a test is needed if dims are critical.

**Nickhofen** · 17-01-2018

Sorry if someone else mention it and I didn't notice.
Have you try with another program? Design the same object and cut?

**toomast** · 02-03-2018

Managed to sort out my problem. Almost too embarrassed to tell but.. as it turns out it is not wise to calibrate machine axis with a dial indicator. At least a machine that has not super accurate ballscrews. Also the testpart that showed inside measures correctly and outside wrong, was coincidence I believe. I re-calibrated my axis with a 300mm caliper. Problem solved.

So anyway here is a little cherry on my strawberry cake:
Material: S335
8000rpm, 350mm/min, DOC 3mm, 2-flute TiAIN 6mm endmill.
Some chatter but nothing major... Shitty workholding. Nice blue chips where flying :)