Newbie looking at 6040 (China CNC) for polypropylene 15mm sheet

**JOGARA** · 10-02-2018

Originally Posted by Snapper

If you're using fusion, use the adaptive tool path for clearing metal out. I've cut down to 13mm Doc with my OMIO, between 0.3/0.4mm step over. You can go wider if you're cutting shallower. Better for tool life too as you're using more of the tool than just constantly using the tip.

Skim off the top of the part so it's all perpendicular to your gantry and spindle then your chamfers should be even. A light rub with sandpaper and a quick splash with polish to remove the tool marks and it will look much better than the grainy texture on the top of the extrusion as well.

I'll give that a go tomorrow.
I am cutting 15mm deep so try 7.5mm at around .5-.6mm step over?

**Snapper** · 10-02-2018

Originally Posted by JOGARA

I'll give that a go tomorrow.
I am cutting 15mm deep so try 7.5mm at around .5-.6mm step over?

Should be fine with that. Just play a bit and see what works. One tip, try and square your spindle to the vice, don't spend hours getting it as precise as humanly possible, just 2 minutes with a dual gauge to get it there or there abouts as it will shift out of alignment anyway within about 30 seconds. I do it before every job I want to look half decent. But if you've been jogging into things it's likely to have got knocked well off and that's an invitation for bad chatter.

Also make sure your spindle, collets and nut are squeaky clean for your finishing tools, and if your collet is old and been bashed about, get a new one. They're only tuppence on eBay.

**JOGARA** · 10-02-2018

8mm DOC, 0.5mm max stepover.
Cut fine, no noise, looks like I can go deeper.
Going to attempt 1mm. Can always pull it back.

This is much better than the 1hour+ than before. Down to 15mins now :)

The spindle is out but only by a hair. I can feel on the contour pass a slight line going around 2 sides of the part.
I have lowered the contour pass to take 4 depths instead of 2, this fixed that problem last time.

I am also getting this again on the contor. I have a 10mm finishing overlap. But I used default lead-in. I have upped that to 2mm. Hopefully that stops that.

And yes, I forgot to go -0.1mm on the contor pass so there is a bur going around the bottom of the part. The roughing pass went -0.2mm, so I normally set -0.1mm for the finishing endmill.

**Snapper** · 10-02-2018

Are you using tooling plate to cut your parts from? That must be costing you a bloody fortune!

**Chaz** · 10-02-2018

Originally Posted by Snapper

Are you using tooling plate to cut your parts from? That must be costing you a bloody fortune!

Its not much more than standard Alu. The fact that its reasonably flat has many benefits.

**JOGARA** · 10-03-2018

Busy week.
Would have been quicker if it wasn't so cold...
Another 2 operations to do in each side and then tumbling and anodising.

**spluppit** · 11-03-2018

I have no idea why you are tumbling parts like this. It's very non standard practice for machined parts of this nature.

**Zeeflyboy** · 22-06-2020

Sure that’s not due to backlash?

Other than improving the backlash situation, the only answer to that is backlash compensation in the control software.

To square the gantry the best I found was to drill 2 holes for precision dowels in the y axis and butt a precision square up against it. I then run a dial indicator along the edge in X axis, and then loosen the gantry bolts and smack it with a mallet until it’s as square as I can get it. You won’t get it perfect as the gantry isn’t completely flat.

**JOGARA** · 22-06-2020

Originally Posted by Zeeflyboy

Sure that’s not due to backlash?

Other than improving the backlash situation, the only answer to that is backlash compensation in the control software.

To square the gantry the best I found was to drill 2 holes for precision dowels in the y axis and butt a precision square up against it. I then run a dial indicator along the edge in X axis, and then loosen the gantry bolts and smack it with a mallet until it’s as square as I can get it. You won’t get it perfect as the gantry isn’t completely flat.

Could well be backlash.
I just measured it again and my 22mm diameter is 0.04 under in the Y and 0.14 under in the X.
It is pretty close but next week I need to do a 190mm diameter hole and close fit a bearing in it.
Yes I am using a caliper... Need a bore gauge.

It is not as off as I thought but if I can get it close as possible, would be less nervous about the big part.

**JAZZCNC** · 22-06-2020

Originally Posted by JOGARA

Could well be backlash.
I just measured it again and my 22mm diameter is 0.04 under in the Y and 0.14 under in the X.
It is pretty close but next week I need to do a 190mm diameter hole and close fit a bearing in it.
Yes I am using a caliper... Need a bore gauge.

It is not as off as I thought but if I can get it close as possible, would be less nervous about the big part.

You can't measure a bore with calipers and believe that 0.04mm measurement or even the 0.14mm for that matter..!! . . . Only a bore gauge can do that with any accuracy.

Also, it's not just the gantry squareness you need to worry about, the spindle tram and parallelism of the rails all come into play and I know for sure that these machines are not good enough in either of those areas to machine a bore that size to any decent accuracy.