My adventures with a bench top CNC mill

[JasonBModerator @jasonb]

A bit more about finish cuts which may be of use to you John in the future when deciding what to use.

Like Julie I often use what F360 calls an adaptive cut to rough out most of the waste. As the tool is making a series of cuts back & forth you wo end up with scallops or cusps when doing internal spaces or fillets when cutting away the material outside of a feature. In this case a follow up contour is generally needed as that will in the case of the two oblong cutouts on the clamps follow a half circle at the ends and a straight line between.

I did not try an adaptive for these two features but based on trying it for the sloping areas where it was taking 3-4 times as long as a pocket due to the small cuts this machine is going to be limited too and the fact that running the free version of F360 means no rapid moves which you tend to get more of with adaptive paths I feel the contour and pocket options are likely to be the best bet for this jon on your machine.

My usual method for adaptives which seems to work for my machine is to leave 0.3mm radial material. I then run a contour with one roughing pass at 0.2mm and a finish one that takes the last 0.1mm off. Again given the lack of rigidity of your machine I would think an additional spring pass at the same final setting would be needed to take out any flex in the tool and machine.

But as you say it’s a practice piece and the other thread would have been very long if all options had been covered, 3000 words and 50 images was enough for me. As I said several times without knowing what sort of cuts the machine will be capable off it is impossible to give an exact approach as there are so many variables involved, so what may work on one may just stall another, the helical entry being just one example.

[John HinkleyParticipant @johnhinkley26699]

Jason,

Once again, thanks for the input.  I’ll file those thoughts away for the moment as my brain is beginning to hurt.  I’ve taken on board what Engine Builder has said, as an experienced Carvera owner and this morning I reworked all the operations with a 3.175mm (⅛ inch) bit as supplied by Makera and recommended by Engine Builder.  This will entail replacing the 4mm collet with the original ⅛ inch one, which is a simple job, and means that the 2mm ball end mill for smoothing the ramps will fit straight in as well, just needing the tool height to be verified.

John

 

[Julie AnnParticipant @julieann]

A few more thoughts:

• The shank of the cutter can always be shortened to decrease stickout
• Roughing/finishing doesn’t take more time, the same amount of material is being removed, but generally a better finish will result. While I don’t build to exhibition standards I like things to look right.
• For long features like the slot I wouldn’t ramp down using a helix; I would use a straight ramp. The performance of helical ramps is very dependent upon the ratio of tool diameter to hole diameter. Ideally the tool needs to be about half the hole diameter or less.

Julie

[John HinkleyParticipant @johnhinkley26699]

Good point about shortening the bit, Julie.  Obvious if you think about it, which I didn’t!

When I make something worth looking at, I’ll use the roughing/finishing technique to get a better finish.  Like you, I appreciate the aesthetics of a product in addition to its utility. All good information to know.

John

 

[JasonBModerator @jasonb]

Any more swarf been produced John?

[John HinkleyParticipant @johnhinkley26699]

I decided to take a step back and reworked the tool paths, taking on board the various suggestions that have been made.  As I’m also making videos of my efforts, I need to take that into account as well as it slows me down a bit trying to get decent shots without long, boring repetitive sections. Then, two days ago my desktop computer took it upon itself to fail.  This coincided with a Microsoft update and an update to my video editing suite.  That has taken me two days to sort out but I’m back up and running again now.  I have some footage of the next couple of operations and hope to publish these today or tomorrow.  I’ll put a link in this thread when I do.

Suffice to say, the operations to mill the slots and roughing the slopes have been done and today’s efforts will see the smoothing operation completed.  You won’t be surprised to hear that there were a few stumbles along the way, but that’s all part of my learning experience.  Trouble is, any lesson I learn is usually forgotten in a couple of days.  It took me nearly an hour just to get the computer to connect to the mill by wifi the other day.  When that sort of thing happens, I get frustrated with it and walk away for a while.

Add to that, a number of medical appointments and the delays all build up.

Rest assured, I’m on the case. It may take me a while, but I’ll get there in the end.

John

 

[Julie AnnParticipant @julieann]

It can be frustrating, but hang on in there. By way of encouragement I managed to CNC mill this liquid cooled power electronics heatsink on my CNC mill a few months after I’d bought the mill:

Granted I was experimenting with the CNC mill every day making simple parts. But before starting I had zero experience of CNC milling and zero experience of CAM progamming, albeit I was conversant with 3D CAD.

It just takes perseverance!

Julie

[John HinkleyParticipant @johnhinkley26699]

Thanks for the encouragement and well done, Julie. Impressive stuff. You have not only engineering training and experience on your side, but youth as well. I’ll be happy if I can knock out a few good looking bits and bobs without too much grief.

John

 

[John HinkleyParticipant @johnhinkley26699]

As promised, and despite continuing problems with my PC, I’ve published the latest video in the saga.

No spoilers, you’ll just have to sit through it like I did to find out what actually happened. (Or skip through to near the end.)

More cnc milling

John

 

[JasonBModerator @jasonb]

Thanks for the update John. It is actually giving quite a nice finish and not too much in the way of high pitch chatter from the cutter.

It will take a while to get a feel for what depths of cut and feed rates work in various situations on any given machine so keep a note of what works and then you can use the same again or try a bit deeper if you felt it could be taking more off.

[John HinkleyParticipant @johnhinkley26699]

Precisely so, Jason. I’ve ordered a couple of 2mm diameter carbide ball end mills from Rennie Tool Co. which I hope will arrive either tomorrow or Monday as backup.  I think that when I set the Z-probe zero position, it wasn’t sited correctly so it started off diving too deep into the workpiece before I realised and by the time I hit the emergency stop button, the cutter had already broken and pinged off into the enclosure.

I hope to get out into the workshop tomorrow to finish the job and take more videos – as long as I remember to press the record button!

At least my PC seems to be working OK now and the editing suite is behaving.

John

 

[JasonBModerator @jasonb]

Make sure you have the tool ctr set to be outside the boundary. That way it will start taking light cuts as it works its way across. If you don’t do that at beast it will have the ctr on the boundary so the first cut will be 1mm wide.

set outside =0.1

And the first cut

If set on ctr a much bigger first cut

[Mark EasingwoodParticipant @markeasingwood33578]

Well, I am impressed by the results achieved on the Carvera Air

Thank you John for taking the time to film and share your adventures.

The YouTube video below popped up in my feed, it is only 17 minutes long, but does give the feeds and speeds being used to machine 30mm thick aluminium with a 42mm long single flute DLC coated cutter, so it may be worth a look.

Mark.

[John HinkleyParticipant @johnhinkley26699]

Jason,

I’ll do as you have suggested with the extra offset.  Luckily I read this post before I loaded the latest iteration of G-code ready to break another cutter.  Postie is due to deliver the new bits this morning so I’m hopeful that I’ll be successful.

Mark,

That looks an interesting video.  I’ll watch it later when the interminable football is on.

John

 

[John HinkleyParticipant @johnhinkley26699]

Mark,

I didn’t wait for the football, so I watched that video while waiting for the morning post.  I thought that he was pushing the machine more than I would care to until I saw the little “4x” in the bottom right corner. Handy to see the speeds and feeds listed, too.  I wondered how the last operation was carried out with the workpiece apparently just sitting on the wasteboard until the end where the sticky tape was shown.

Jason,

When I checked, the offset that you highlighted was already in place.  I didn’t put it there I don’t think, so perhaps it’s placed by default to help people like me!

John

 

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