Lead in and lead out with line cutting and tab holding.

[D3workz]

Hello people.

So, I am new to sheetcam but I am coming from a Fusion360 back ground. I ve been using Fusion for over three years and I finally made the switch to SheetCAM which with out any hesitation its by far more superior for plasma operations.... However I am a bit disappointed as to why sheetcam does not include lead in and lead out when cutting just a line or with the holding tabs function (I ve been trying everything LOL).

If there was nothing great about Fusion, the holding tabs option was really refined. Is it possible that none of you guys use holding tabs or lets call them multiple starts on same object? And if you use the holding tabs as is currently in sheetcam, do you stop your torch and re fire your torch on your edge of the part that you are cutting?!!

Also, is it possible that one cannot import a simple line and decide if the tool path includes the kerf width, i.e. apart from cutting on the center of the line, one chooses to start on the outside or on the inside of the line (I mean when it is not a closed polyline/object).

To say everything, I did manage to create a proper ''holding tab'' by using perpendicular lead in and lead out with a negative overcut (this would lead out and stop the torch away for the part's edge and pierces away from the edge and leads into the original cutting line, thus no divets induced but leaves a tiny tab to be cut with a grinder later). Now, if this could be made as an option for ''multiple start points'' thought out the part, one could cut long and narrow parts without denting the edge from the pierce and minimize warping and bending as the part would be held at intervals with the stock material.

Finally in lieu of all the above, it could be that I have missed something in sheetcam and I am reading the holding tabs function wrong!!

If you like, I can include examples for what I mean.

I ll wait to see what you think.
Thank you all.

Dim

[WyoGreen]

Hi Dim,

I personally have never used holding tabs on my plasma table. The torch never touches the material to drag it, so why would you need holding tabs? I suppose there are occasions where tabs might be needed, but I've never encountered any. Now I do use holding tabs when routing, but there the cutting tool is touching the material.

As far as the lead-in and lead-out question, I really have no thoughts on that. I cut very few open lines, and when I do, I just cut them however Sheetcam wants to cut them.

Have a good day, Steve

[D3workz]

Hi Steve,

I use holding tabs for two scenarios.

one - When I have hundreds of small parts to cut from one sheet and I use holding tabs to prevent these small parts to drop in the machine's undertray. If these parts are let to fall, they become full of molten pieces of steel and I ll end up cleaning all the parts, apart from having to collect the pieces from an awkward place.

Two - Its very frequent that I cut long parts, example parts that are 80mm wide and 2m long (for stairs and balconies etc). I place taps along the part to minimize movement and warping.

To repeat myself, the first issue I managed to solve as sheetcam accepts a negative overcut which literally leave a small piece that is uncut, hence the part would stay attached to the stock material... but for the second scenario I am not sure what sheetcam can do.

How do you go around cutting long and narrow parts with out distortion ?

Thanks

Dim

[Les Newell]

In your cut operation turn on 'Offset open paths'. You can now apply kerf compensation to lines. To change the offset side move the start point to the other end of the line.

[D3workz]

Ahhhh... so there it is, and even the option of having the lead in and out! my apologies, but I did not notice (new to sheetcam).

At least I can prepare 'tabs' from cad which will leave a tiny uncut pieces.

So, one last thing (it might not be a question of ask in this section but here goes).

Whilst racing though the buttons of sheetcam tying to find the lead in and lead out for a line , I found the Edit action points tab and notice that for a particular distance, I could greatly increase the feed rate.

Do you think that if I rapid the cutting for lets say 10mm, would this create like a holding tab (since in that rapid move the plasma most probably would not cut though)? Or I am misleading myself? because if it does it would be cool to have a holding tab with the benefit of avoiding an other pierce!!!

Thank you so very much guys.

Dim

[Les Newell]

That thought occurred to me a while back but I never got around to testing it on my plasma. This method has the advantage that the tabs are scored, making them easier to break.

I think the biggest question would be if it would pierce properly when it slowed down after the tab. My feeling is that it would work for thin materials but no so well for thicker materials. It also depends on how fast you cut. If you have optimised for cut quality there will probably be enough overhead to punch though. If you have optimised for speed, maybe not. On very thin materials you may find your machine cannot move fast enough to get it to transition from cutting to scoring the tab.

If you experiment with this I'd be very interested to know the results.

[djreiswig]

You may also have problems with wrecking your consumables from the blowback when it's not cutting through.

[Les Newell]

Hopefully that shouldn't be too bad. As the torch is moving fairly fast the splash back should mostly move backwards rather than upwards into the torch. I wouldn't recommend using a drag torch for this application. Thinking about it, if you have THC you may have to lock out the THC as well. Then again, having the THC raise the torch a bit while scoring the tab may be a good thing. Lots of potential experimentation options for an intrepid explorer!

[D3workz]

Thanks for all your input guys.

Since I am used to using tabs a lot, I will experiment with this rapid thing and I will tell you the results.

I think I ll experiment with two action tabs. the first one will be a rapid one and right after I ll make another with lets say 60% to 80% cutting speed. Both will have a short duration of around 5 to 10mm. I think this combo might create holding tabs and avoid and extra pierce.

Regarding the THC, first of all at the moment my THC cannot be set from Gcode (but this is a future upgrade) and since I usually cut heavy steel (from 6mm to 12mm) my sheets are fairly straight and the THC is set with a low sensitivity so it do not give me any issues from diving into the work...in fact its not ever a concern (but this will be changed in the future now that I am using sheetcam).

I ll make some experiment and get back in a couple of days.

Thank you all,

Dim

[D3workz]

So yesterday I tried the action command and on 2mm steel it worked brilliant (see image).

I set one as a fast rapid move of 500% for 10mm then right after I set a 5mm move with a 70% feed rate. The operation was flow less, you wouldn't notice the machine actually doing it.. next time I ll try on thicker steel, as I think the trick on thick steel is to slow enough after the rapid move to give time for the torch to actually continue the cut.

N.B - on 2 mm thk steel, there was no blow back.

I keep you posted.

Thanks

Dim

[Les Newell]

Thanks for reporting back. That does look pretty good. I'll do some experiments myself. If it works out well I'll look into adding this as an option for holding tabs. That would save the hassle of having to set up two action points for each tab.

[D3workz]

Hi Les,

Thank for your reply.

Tomorrow I have in mind to experiment with some 8mm thk steel as I need to use tabs since I ll be cutting long and narrow parts (what I cut the most). Thus I ll be experimenting on some scarp metal. I ll let you know what happens with settings I try.

Thanks and regards

Dim

[djreiswig]

Nice job. That eliminates the dimple from an extra pierce.

[D3workz]

So as promised I did some further testing, this time on some 8mm thk mild steel.

So the first issue I found was that in sheetcam if you try to use the action tab feature on a lines with no kerf offset, the action tab feature does not work well. It does not take into account the distance but simply modifies the feed rate at keeps it modified. After a while I realized that for the action tab to work, one needs to have kerf offsets or cutting on the outside or the inside of a closed shape. I think this is a bug, maybe you can look into it.

Apart from that, I did many testing and realized that actually with only the rapid move, the tab gets created and its kinda irrelevant if you try and slow down the feed rate right after the rapid move! I think its not needed.

If you see the attached image, that is a photo take from the underside of an 8mm thk steel plate, where I was testing. If I had to discuss blow back, the tabs created in the red circle did create some blow back which was noticeable, but as Les mentioned, it did not ever touch the shield cap. The tabs in the yellow circle are ever milder. Usually I cut 8mm thk steel at 1.5m per min at 70amps, and I think running an 8mm rapid of 190% speed is the best solution.

Thanks Dim

[Les Newell]

Thanks for your test results.

So the first issue I found was that in sheetcam if you try to use the action tab feature on a lines with no kerf offset, the action tab feature does not work well.

That definitely does not sound right. I'll look into it.

Apart from that, I did many testing and realized that actually with only the rapid move, the tab gets created and its kinda irrelevant if you try and slow down the feed rate right after the rapid move! I think its not needed.

If that's the case it should be pretty easy to add an option to tabs that simply rapids with the torch on.