I will buy a cnc router and i have the choice of adding to the router a drag knive : https://www.youtube.com/watch?v=bMoRUZnvbXw
or an oschilating knive : https://www.youtube.com/watch?v=5irxBCBFoOY
I want this for cutting forms of prepreg carbon fiber.
Do you have any thoughts or knowledge about which one of them would fit best the perpose ?
Do you want to cut cured or uncured pre-preg?
Thank you for your interest as always Hanaldo .
I want to cut forms of uncured prepreg .Actually i want to use my
router as substitute of the far more expensive machines that do only this
job.
Never had any trouble with drag knife the only thing you find is depending on what material your cutting you can loose the edge on the blade fairly quickly
We use carbide inserts which are sent off an sharpened in batches of 20
You need a really good airbed on your machine and ideally you want your material supplied plastic/plastic backing, paper can rip/pull/tear/lift and basically be a pain !
Good addition is a pen holder (simple Sharpe marker will do) so you have your kit marked up
When you end up with several hundred bits cut out but some with different orientation,staggers an ooverlaps saves a lot of confusion
Hardest thing is your nesting programme,all the early machines came from the steel/laser cutting industry where you haven’t got to worry about orientation,weave stripe,flipping your material so its handed once you have digitized your template
I unfortunately dont have an automated cutting machine! Do drag knives tend to ‘clog up’ more when cutting pre-preg as well as lose their sharpness similar to hand knives? I imagine this wouldnt be as much of a problem with an oscillating knife
No they don’t tend to clog up
They are cutting at a faster speed than you would by hand so doesn’t really happed. Also your blades always at the perfect angle
With everything thou its trial and error, you have to alter your cutting speed to suit your material to avoid issues
Ah cool thanks Rob.
Be aware that professional prepreg cutters use rotary cutters, instead of dragging blades. The rotary blade lasts much longer, is safer for the tabletop integrity and cause no catastrofic (fiber dragging!) troubles whether the blade is not sharp enough to cut through the whole fabric thickness.
Be aware that not all professional machines use rotary cutters !
Many professional machines out there using several different methods of cutting
Some of it depends what shapes you want to cut out
Motorsport for example some of the shapes,corners and details you could never do with a rotary blade
Yes, as you said, just some of the shapes. 90% is cut with the roller blade. Unless you want to change the blade every 50m. of cuts.
Using proper carbide blades getting sometimes a weeks worth of cutting out of one blade cutting several rolls of material and many many meters of cutting
i use both on a the cutting machine i operate. Cutting prepreg of course.
It depends on what the backing material is like on the prepregs. Some stick well and give no issue with the drag knife. Some come off easy and so I use the oscillating blade. Both last a long time. The oscillating blades i have are more like tiny little sword shapes, very fine point, for very detailed cutting. I also often cut templates for scribing and trimming.
if i had to choose one, i’d go oscillating for sure. Covers more material types. Less resistance through the material. Try cutting high mod uni with the regular drag blade… bleh.
for longevity, the roller blade is probably better. I don’t use it cause my machine has a conveyor and i’d need to install the plastic shield to use it. There are also powered rotary blades available as well.
Snap !!! I am planning to cut high modulus prepreg … it doesnt look good but i have no choice since the machine i will use can only take drag knife - no oscillating … you mean it is difficult? (bleh) or it is not possible ?
hmmm… well. It might be possible… though, very difficult with a drag knife. I"ll bet others have done it. But on my machine the knife generally only creates a mess as it cuts across the fiber, it tends to rip things up and pull the material. In reality, a rolling cutter would probably be the best for uni; as it would have the least resistance. Can you use a cutting wheel instead of the knife? I use the oscillating blade because it’s there and I don’t have to change anything to make it work. It’s also not the best, but very usable.
Is your prepreg double plastic ? Paper backing causes a lot of problems lifting
Also you might be cutting too slow ? People get problems,slow the knife down when they should be doing the exact opposite
Knife depth and set up are also crucial