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CNC metal machinists (for Stax amp cases) unite?


jamesmking
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Posted (edited)
11 hours ago, Kerry said:

Congrats!

Thank you Kerry, however, yesterday I then tried an uncoated 2 flute 2mm slotting endmill... the results was not good at all.... very poor chip evacuation and lots of chips welding to each other. Almost no chips get thrown clear of the cut. I'm not sure if the end mill is garbage or if something else is wrong.... I was looking online for some kind of guide that had photos of poor results and what to do about them... but there seems to be very little information other than feeds and speed calculators which seem to suggest parameters that I cant get close to.

I tried to extrapolate settings from the great results I got from the single flute 2mm end mill to a single flute 3.175mm end mill but to no avail. The 3.175 end mill could not run at anywhere near the rpm or depth of cut of the 2mm end mill without welding, vibration and large burns on the edges of the cut.... Perhaps the 3.175mm end mill is just crap (its not the same brand as the 2mm)... 

wow cnc aluminium is frustrating...

Edited by jamesmking
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James, make sure you use the best possible (carbide coated) cutters and also keep in mind 1.5kw is not that much when you calculate speeds. Make sure cooling the bits and material while cutting is adequate as well.

Looks like it is getting pretty hotm here, cutter is not good enough or speeds are too high.

Edited by audiostar
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Posted (edited)
1 hour ago, audiostar said:

Which aliminium alloy is this exactly you are working with?

6061-T6 being the standard for CNC machining and excellent all purpose alloy.

i have no idea of the type of aluminium, its a disapante case I purchased some time ago from modshop. 

The fact I got such good results with a 2mm end mill, especially on chip removal and surface finish on it makes me suspect the 3mm end mill is just crap (the 3mm comes from a different supplier and is a different brand to the 2mm). So I have ordered some 3mm end mills of the same brand as the 2mm.

The spindle does not seem to be slowing down, vibration was low, cutting noise was low and I did not use any coolant with the 2mm...

as far as I can see if I can go 300mm/min 1.6mm depth of cut on a 2mm end mill with zero issues, low cutting noise and no lubrication,
(I managed to break it at 500mm/min 1.6mm DOC but I was deliberately seeing how fast I could go), I should be able to do similar with a 3mm end mill of similar geometry (both single flute and both DLC coated)... but the best result I got with the 3mm was 0.2mm DOC, poor top edge and much reduced rpm compared to the 2mm. Any time I tried to increase the rpm chip welding became worse and chip evacuation did not improve, any DOC above 0.2mm I got lots of vibration and nasty noises.... looking carefully at the cutting the 3mm was not pushing material up the flute instead material was wrapping itself around the outside of the cutter and then welding itself to the top edges of the slot. I did not seem to be cutting so much as ploughing. Slower feeds resulted in the chips becoming like power and welding themselves all over the cut like fur... I tried cutting oil with the 3mm and this did not stop the welding.

Feeling the edge of the flutes the 2mm feels super sharp all the way up whereas the flute the 3mm only feels sharp right at the bottom tip of the flute and the rest of the flute all the way up does not feel more than moderately sharp. I suspect this is why I cant get any sort of depth of cut. Even plunge cuts at the beginning of the slotting sounded much nicer on the 2mm than the 3mm end mill. (plunges straight down at 25mm/min)

 

 

Edited by jamesmking
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On 8/29/2022 at 2:38 PM, audiostar said:

Hi James,

from your detailed description, it looks like the cutter being the culprit. It would be the first to swap out.

Things are looking up again... I just took delivery of some 6mm single flute DLC coated end mills, selling says they are designed to cut aluminium without liquid lubrication. Initial testing looks very good, absolutely throws chips out of the cut into near earth orbit when doing a full width slot. Zero chip welding. Surface finish as good if not slightly better than the 2mm end mill (So far got the speeds and feeds for the 6mm up to 400mm/min feed rate, 1.5mm DOC and 11K rpm). Cutting is very quiet and almost silent at 1mm DOC... The vfd and control box fans are louder than the cutting noises. I am sure there is much more to be got out of this end mill, but I'm progressing conservatively because these 6mm end mills  are not cheap and I don't want to push it to destruction. 

The biggest take away for me is that buying cheap end mills from the manufacturer of the cncs website is not the best move and that end mill quality absolutely radically effects what you can do. I also think i'm going to invest in a oil/air mist system...

IMG_20220901_112055958.thumb.jpg.2b5d6ad56637176412c8d80ecd52b7ff.jpg

(the hideous grey mess is the 3.175mm POC (piece of crap) end mill WITH cutting fluid dripped onto the cut... :tmonk:.) 

middle slot is 6mm end mill 1.5DOC 3mm total depth 11Krpm 400mm/min no cutting fluid no finishing pass no deburring...

front slot same settings as middle slot but 1mm DOC and 10Krpm.

 

 

Edited by jamesmking
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First attempt at a complete front panel. Single flute 6mm end mill and 0.1mm V bit used. Depth of cut 0.02mm on the engraving. I also used tape and CA glue as the hold down method for the first time - I really like it. Much less vibration and far quieter when cutting in the middle of the work piece compared to just clamping the corners. As usual no deburring or finishing pass. The surface finish on the volume pot pocket is silky smooth - the photo does not do it justice. Very happy with the results. Not so happy that I have zero artistic talent for cool looking front panel designs....

IMG_20220905_142214856.thumb.jpg.662ba66bf534ae69ce46620bd4a26553.jpg

 

 

IMG_20220905_142242287.thumb.jpg.92ab78bc8cb6f4a8dfda7d7856788c67.jpg

IMG_20220905_142258927.thumb.jpg.19fbf438a28e510cf7eb6b39d6f72941.jpg 

Another go at a Stax socket with the better quality end mills. Much better surface finish than my previous attempt cheapo mills and I'm using faster feeds and speeds this time. Just shows that a crap end mill gives inferior results even on soft plastics. There are no burs around the edges of the cuts and the surface is smooth.

IMG_20220906_192703559.thumb.jpg.3c3911aa9de748ee17a59f7aea38c863.jpg

Edited by jamesmking
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5 minutes ago, n_maher said:

Looks awesome to me.  I mean you could add a logo of some kind if you come up with some artwork?  I’m not 100% clear on where the required blue LED goes.

REQUIRED blue led is the blue ring around the power button on the power supply....

 

Edited by jamesmking
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That panel looks good. Is it for an original DIY T2 or a Modified DIY T2?

 Me to have done some milling.

 90630041_IMG_0486(002).thumb.jpg.887f0de665345353cde9a2bdc6f18529.jpg

0.38 mm end mill, 18000 rpm and 300 mm/min. Two sides, 121 holes (5 diameters) and cutout took a little less than 2 hours.

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10 minutes ago, JoaMat said:

That panel looks good. Is it for an original DIY T2 or a Modified DIY T2?

 

mostly modern T2 or possibly fully modern if the tta/ttc substitution for the 79 and 216 proves to be reliable. I don't think I will ever build an original.

Edited by jamesmking
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tta/ttc and kca1220/ksc2690 are, in my opinion, reliable. I've used them for years as substitute for j79/k216.

 Next step is the 37 vias.
1998534575_IMG_0487(002).thumb.jpg.8334c33b67bbc23daa526bf2be82f617.jpg

 Board, 0.5mm wire and tools. Anyone prepared to pay a fortune for handmade printed circuit board?

 

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  • 1 month later...
Posted (edited)

T2 psu back panel, design and cut. I wanted to have the pin outs of the sockets for the umbilical chords from the psu to amp to be on the psu back for future reference..

I decided to go for 10degree 0.1mm tip engraving bit for the lettering, 0.025mm depth of cut rather than laser. Screw holes done with 3.175 end mill and main cut outs 6mm end mill. Now I have a good collection of quality bits and little experience now. CNC machining is starting to become FUN 🙂. Its so much nicer and more satisfying watching a CNC cut than using a hand drill and Dremel... Tool changing is a bit of a hassle and then I have to use a Z block and Z probe command get the new Z height reference for the tool sickout. So I try to minimise the number of different tools used.

2143108423_2dview.thumb.jpg.422c40e5c788d17bdd2071d98f6303b1.jpg

591489925_3dview.thumb.jpg.cbd9d90818b314fcecb4b6779b04afde.jpg

Tape hold-down and CA glue works perfectly. I'm very happy with the surface finish, perhaps the text for the pinouts and lines could be a little narrower, but its certainly not a disaster. Cut still currently in progress:

 

IMG_20221009_175931269.thumb.jpg.6a10e6cd6d285afacfc95833d2ee5131.jpg

The nice thing about symmetrical panels is that you can always adjust your settings and have another go with the other side...

I decided to decrease the line width by half, nock 20% off the size of the socket decals, decrease the socket decal font size, change the style of the lines and reduce the engraving depth from 0.025 to 0.02mm... 

2d.thumb.jpg.55246b5a7b2b6d4044bdcfdb587cfe99.jpg

3d.thumb.jpg.c8b6b0ca83f33d005dfc8f400ee54782.jpg

I think the new version should look a little less blocky and a bit more refined... The 0.02mm engraving depth is slightly too little, other than that I think its an improvement.

IMG_20221009_223913809_HDR.thumb.jpg.274b23c79084dcfab15452bef3934606.jpg

Edited by jamesmking
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