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Cutter knife and... gum?

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Giulio Buccini
(@julius)
Beiträge: 212
Reputable Member
Themenstarter
 

I've no experience in using a cutter knife on a cnc-router, I hope that someone of you can answer to my question: it is possible to use the cutter provided from Stepcraft to cut a rubber-plate 1.5mm thick?

I'm talking not about hard-rubber material (i.e. vulcanized gum) but flexible rubber with hardness around 60-70° Shore-A. In particular, I'm worry about making 90-degree cuts, how can it be done with a knife?

I found a video on youtube, here you can see the cnc-machine making cut that I want by simply lifting up and down the blade. It is possible to do something like that with the Stepcraft cutter?

Cutting Leather With The Donek Drag Knife

SC300 + Spindle HF500 + Portalerhöhung + LinuxCNC + gsimple

 
Veröffentlicht : 11/05/2015 1:43 am
Andreas
(@magio2)
Beiträge: 2619
Famed Member
 

The tool in the videos is a little bit more professional. The cutter can be turned by software/controller. The SC cutting tool is turned while cutting by the cutting forces.

I did not test it up to now, but Inkscape nowadays has a nice feature to export a file as HPGL. The export tool behind allows to do the correction for cutters that cut behind the center. This should give you a file where 90° turns produce real 90° corners. Maybe this together with a "dive into" to set the knife in the right direction would give the best results on the SC.

I am not sure how deep the SC cutter tool can go, but my gutt feeling tells me that 1.5mm might be too much. And with rubber I'd expect even more problems. If you have a look at the image of the replacement knife, you see that the sharp edge turns into a cylinder very fast. This would give you a lot of friction in rubber.

SC 420 mit DIY parallel + Proxxon mit Mod + HF500 + SprintLayout + LibreCAD/QCAD + FreeCAD +WinPC starter/USB->EstlCAM + EstlCAM LPTAdapter + EstlCAM Handrad + DIY Vakuumtisch

Gruß, Andreas

 
Veröffentlicht : 11/05/2015 9:45 am
(@pyromane)
Beiträge: 137
Estimable Member
 

The tool in the videos is a little bit more professional. The cutter can be turned by software/controller. The SC cutting tool is turned while cutting by the cutting forces.

Pay attention to the mother, who does not move. Therefore, it is a normal drag knife , similar to the SC.

 
Veröffentlicht : 11/05/2015 10:36 am
Andreas
(@magio2)
Beiträge: 2619
Famed Member
 

Wow .. that's cool then. So it must do tiny little movements while going down into the material?!

Well ... I think that this can't be done with Inkscape -> WinPC NC toolchain, as the HPGL-file does not support different heights. In the video it looks like there is one height for moving without cutting, one height for turning the knife and another height for cutting.

Maybe it works with Inkscape -> EstlCAM ?->
and the feature to dive in?

Would be nice to have a file created by SheetCAM for analysis. :whistle:

SC 420 mit DIY parallel + Proxxon mit Mod + HF500 + SprintLayout + LibreCAD/QCAD + FreeCAD +WinPC starter/USB->EstlCAM + EstlCAM LPTAdapter + EstlCAM Handrad + DIY Vakuumtisch

Gruß, Andreas

 
Veröffentlicht : 11/05/2015 4:13 pm
Giulio Buccini
(@julius)
Beiträge: 212
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Themenstarter
 

The description of the SC dragknife reports: "angular degree: 60, suitable for foils over 0,5 mm"
But it's not clear if 1.5 mm of rubber can be cut or not. Mmmmh...

As I understand, the trick for the cutter in the video is to program movements in such way that knife can be rotated in any cut-direction.

For example, to make a 90 degree corner:

0) the router reaches position A
1) the router stops
2) the router lift up the blade, but in such manner that the tip still touches the material
3) router makes a smooth rotation, dragging the tip of the blade in A and, at the same time, rotating the direction of cut.
4) the router reaches the B position
5) the blade is pushed down again
6) the router starts to cut along the new direction

The trick is to maintain the tip of the blade in contact with material so it can be rotated exploiting the offset (i.e. the horizontal distance between the tip and the vertical axis of the router)
As I can see, this movements can be programmed by custom G-code (obviously this approach holds if you have to do only few cuts, for complex shapes programming all the work manually it's a nightmare).

SC300 + Spindle HF500 + Portalerhöhung + LinuxCNC + gsimple

 
Veröffentlicht : 11/05/2015 4:58 pm
Giulio Buccini
(@julius)
Beiträge: 212
Reputable Member
Themenstarter
 

I suspect that the steps I wrote are not completely correct. When the cutter is lifted up in A a little amount of material in the corner remains uncutted. mmmmmh....

SC300 + Spindle HF500 + Portalerhöhung + LinuxCNC + gsimple

 
Veröffentlicht : 11/05/2015 5:01 pm
Andreas
(@magio2)
Beiträge: 2619
Famed Member
 

That's nearly what this inkscape plugin for exporting to HPGL is doing. The part missing is the "lift up but still touch the material" is missing due to the fact that HPGL only knows 2 states "pen up" and "pen down".

For the procedure described by you, you'd need 3 states "pen up" (for moving to another line), "pen down" for cutting and "pen in the middle" 😆 for doing the turn.

Someone from the german part of the forum who tried this inkscape plugin with foil said that it works fine. But of course this is not how to cut thicker material at all because the knifes blade might break.

Rubber ... I don't know ... maybe it does not break the blade, but minimum I'd expect is, that it will look ugly.

SC 420 mit DIY parallel + Proxxon mit Mod + HF500 + SprintLayout + LibreCAD/QCAD + FreeCAD +WinPC starter/USB->EstlCAM + EstlCAM LPTAdapter + EstlCAM Handrad + DIY Vakuumtisch

Gruß, Andreas

 
Veröffentlicht : 11/05/2015 5:49 pm
(@mrmajo)
Beiträge: 526
Honorable Member
 

Looks really interesting.

On the webpage of Donek Tools you can get a free tool (excel sheet) to convert the normal g-code to a version with adjusted radius in the edges.
http://donektools.com/free-cnc-router-software/links-2/

As well the tool is asking for a "swivel height". Maybe this tool is doing all the needed work?

Thanks,
Marco

Gelernt auf Stepcraft 420
Jetzt mit der Sorotec AL-1107 unterwegs.

 
Veröffentlicht : 11/05/2015 5:55 pm
Giulio Buccini
(@julius)
Beiträge: 212
Reputable Member
Themenstarter
 

Ok, so I think that I will abandon my idea about cutting rubber.
Anyway I've discovered something new about usage of the routers as cutters.

The idea of a post processor for G-code is good, but probably the one proposed from Donek is suitable only for their tool, mainly 'cause of the particular geometry of the tool itself.

Just for the chronicles: today I've cut a 2mm thick plate of vulcanized rubber (german: Ebonit?) with a 2-flute, 1.5mm dia, carbide end-mill (I know, I'm crazy).

feed rate = 120 mm/min
doc = 0.5 mm
rpm = 7000

It cuts the rubber with zero problem (neither temperature problems nor sticky gum on the tool). The gummy is "pulverized" by the cutter and the quality of the resulting "cut" is not so bad (in my opinion). Obviously, trying to cut a soft rubber in the same way it's almost impossible.

SC300 + Spindle HF500 + Portalerhöhung + LinuxCNC + gsimple

 
Veröffentlicht : 12/05/2015 1:17 am
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