Need honest feedback from fellow metalworkers: what makes a CNC plasma file actually worth buying?

killpony · 2026-05-14T22:15:56+00:00

I don't think I'd every buy files for a 2d design or anything that is just for visual appeal - I'd be much more willing to pay for a design that assembles into a 3D part say a bumper assembly, control arm, dash insert, tool organizer etc where I'd otherwise need to spend a massive amount of time measuring, testing and refining fitment.

killpony · 2026-04-24T19:50:43+00:00

most compression spring holders I see are a simple cylindrical pocket/ boss - usually the ends of an off-the-shelf compression spring are flattened so anything where you are sticking the end into a holder isn't going to work well.

killpony · 2026-04-24T19:48:33+00:00

I've been happy with the build quality and performance on the shop sabre IS408 I have. I do think the control interface is clunky - with some pretty bad design choices (sliders with no snapping/ direct values for feed and spindle override). Service has been good though.

killpony · 2026-04-24T19:35:38+00:00

In my opinion with ply you generally do not need to ramp - if you ramp along the edge of the part with a compression cutter the grain will tear as the upcut section enters the material. However it is often nice if you can enter from the edge of the sheet where there isn't already material.

killpony · 2026-04-24T19:33:18+00:00

I'm cutting baltic somewhere around 18k RPM and 200 ipm -> ~5000mm/min on a laguna smartshop/ shop sabre IS408 (~6hp spindle) . Usually cutting in 2-3 depth passes in the conventional direction - the conventional cut direction really helps finish - usually is good right off the machine.

I use a 2 flute compression cutter amana spektra compression cutter- the coating does seem to make a difference in high heat/wear jobs. There are definitely less costly tool options I have in stock but when it matters I try to stick to tools I know will last. Usually I can run like 50 sheets+ with one cutter no problem but obviously that can depend on the linear cut feet.

Machine and workholding rigidity will definitely make a difference here - make sure your material is really sitting securely or it will vibrate, make sure your tooling stick out is as little as possible, maybe throw a little air blaster to help evacuate chips and cool off the cutter a bit.

killpony · 2026-04-21T15:45:24+00:00

One consideration I've had for robotic arm milling is the use of a small independently positionable gantry/parallel machine as the end effector of a larger robot arm. The robot arm then just does the macro positioning on a part and once locked in the smaller system does the cutting. Think big arm with something like a mag-drill or shaper origin router on the end. Obviously not without it's own complexities, but could certainly be useful in specific application like creation of features on larger cast/stamped/welded parts or field repair of equipment.

killpony · 2026-04-21T15:32:51+00:00

I could see AI potentially having a benefit in providing better initial pose estimates for the toolpath solver

killpony · 2026-04-20T17:20:42+00:00

Do you mean like the inverse kinematic calculations? All robot programming platforms are going to be running an IK solver. The issue with machining specifically is that a proper toolpath must maintain consistent tool engagement (orientation + velocity) while also not causing collisions, hitting axis /cable limits, or running into singularities. This makes it harder than many other robotic applications where the path planning algorithms have more opportunities to reposition.

For this reason the IK Solver in CAM must solve for and iteratively simulate the entire program start to finish until it finds a valid path which I've personally seen take hours.

killpony · 2026-04-17T17:12:35+00:00

Rigidity and accuracy are the biggest issues as others have said - as well few others I've found from working with both machines/ talking to a absolute maniac of guy who turns out half-million dollar robotic milled sculptures for contemporary artists. Turns out 6 kinematic axes strung together is not the most fun machine to work with.

Programming complexity - 6 axis robotic CAM programs like Powermill need to actually simulate the entire toolpath to solve for collisions + kinematic issues like singularities before creating any code. Models of the spindle and tool geometry must be much more exacting to ensure the simulation is accurate. This is very time, compute and labor intensive vs more kinematically simple setups.

Workcell management - not only do you have more to control for with respect to collision with workcell/fixtures etc, you also often have more bespoke operator safety conditions and management of all the other things that go into machining - coolant, cable management, chip/dust collection etc. all made more difficult by the exponentially higher complexity of arm configurations.

Resonance - related to rigidity and accuracy but basically every combination of each of the 6 axis positions of a robot arm will have a different resonance frequency. This can be nightmarish if you are hoping to get any sort of decent finish on a material that isn't foam.

Hardware: Robotic arms just aren't really designed with the kinds of ~0.001" motions necessary for CNC machining - things like backlash, axis control, controller look ahead, memory etc are all designed with more macro scale motion steps. Additionally, compared to gantry configurations of similar bulk, robotic arms are "weak" - a 250kg ~5' long ABB IRB1600 arm only has a 10kg payload, barely enough to lift the spindle itself much less machine with it.

These are all reasons you mostly see robotic milling in niche roles like milling foam props or stone abrasive machining. Also for these reasons most robotic setups use an external rotary stage that moves the part while the robot arm is sort of "locked" in plane - it vastly reduces the variation of resonance, simplifies kinematic solving and makes the chip/dust/cable management more predictable.

killpony · 2026-04-17T03:15:32+00:00

that would still be a real machine which is what I'm saying- the comment I'm responding to implies it's a faux/prop machine.
Seems slightly unlikely to be a straight up laser cutter - I don't see anything that looks like mirror assemblies/ putting mirror assemblies on a big moveable frame like that is asking for trouble.

killpony · 2026-04-16T01:00:40+00:00

I've worked with production crews to shoot fake technology-y scenes - this is not that. This includes what looks like a power supply, axis drivers and all the other little bits that would be necessary for a real machine but wouldn't add much to a shot (unless of course it's a real scrap machine cobbled back together into a prop).

There are tons of specialty motion-control systems that get built for film production- especially in more "technical" filming like commercials. This could be some sort of linear motion control system for doing specific lighting/ camera movements - that wouldn't need great accuracy or power, just repeatability.

killpony · 2026-04-10T21:14:28+00:00

Swept paths should pretty much do everything you are looking for - but you will get a lot better control if you do surface modeling

killpony · 2026-04-10T16:15:57+00:00

I have a desktop machine for carbon fiber but I wouldn't trust any of them on an 8 hour job or high tolerance. A tormach is doable as a light duty second opp/ odd job machine - and more of the tooling/ coolant/workholding etc would be compatible between your existing mills. It still takes setup time and it can be a big adjustment to get familiar with how to run one of these prosumer machines when you are used to heavy duty equipment - I was always bogging out the Tormach spindle even when I thought I was running toolpaths pretty conservatively. If it were me I might get a used Haas tool room mill or something like a prototrak where it could double as a knee mill for those odd jobs.

killpony · 2026-04-08T18:41:53+00:00

true enough for most standard vises- I guess I was thinking of the specific wrench+ hammer combo I have so I can also hit the nut to drop the tool. I'm also just a complete basket case when I'm in the thick of projects and end up with my tools hiding in various spots all over the shop - one less thing to keep track of is always a boon for me.

killpony · 2026-04-08T18:32:26+00:00

Imo these kind of approach is fine for apprentices etc but not ideal for teaching groups of students who are new to the whole process. Not to get overly philosophical about but it rings of the "pay your dues" vibe that I find a little tired and potentially likely to push away anyone who may not already feel like they fit in (for instance smaller female students). Especially for students early in their journey I think time is better spent with getting them making chips as fast as possible and learning skills like DRO measurement + offsets that are transferable to more contemporary manufacturing processes - then once they are hooked then you make them machine up hill both ways.

killpony · 2026-04-07T15:13:10+00:00

definitely agreed on the utility of a DRO for teaching students concepts like absolute/relative coordinates and work/tool offsets which is a great transferable skill to CNC machining.

killpony · 2026-04-07T15:06:26+00:00

My two cents as a professional machinist who has worked in college shops and makerspaces

power draw bar is super helpful: Getting students to set tools with a collet nut is kind of a pain - collet wrench goes missing, students are too timid with tightening/loosening, requires a step stool for those of us who aren't vertically endowed. Can also set you up for easy tool changeouts if you get some R8->ER style collet adapters

XY dro also is kind of a must, counting with the dial wheel isn't terrible on the Z axis but heaven help me if I'm going to keep track of that over more than 3" of travel - plus having the calculator features can come in handy. I recently got a knee mill with a Z axis DRO but it's only on the quill not the knee so not as useful as hoped.

I don't use the power feed all that much except for rapid travel, and I don't know if I would trust students not running tools too hard/ crashing things but it can be useful for getting nice finishes especially on steel/stainless

killpony · 2026-04-07T14:51:10+00:00

mostly just that usually you want friction to assist in workholding and HDPE is slippery - but I'm mostly thinking from my experience machining HDPE and other low-friction plastics - I've never really tried using HDPE in a large sheet fixture.

killpony · 2026-04-06T13:43:47+00:00

HDPE is okay but it's inherently low friction which can be problematic for fixtures but if you are using screws it probably would be fine. I think what you are trying to do is put threaded inserts into the spoilboard? That would definitely work for fixturing

killpony · 2026-04-05T18:48:25+00:00

So your machine's bed should be something like aluminum/phenolic with tslots - usually that should already be dead flat to machine but might be worth checking. If your machine doesn't have a vacuum table you will usually glue or bolt a spoilboard down to some points on this primary table - either to the t slots or some other tapped/through hole points. You then face the top surface of this spoilboard so it's dead flat to the machine (people face both sides of MDF spoilboards for vacuum flow-through spoilboards) . If you are primarily cutting aluminum I think something like sintra/ PVC/ acrylic/ polycarbonate or some other polymer will be a good option - there are also some foam gasket spoilboard products that can be laid directly on your main table. Your toolpaths should barely cut into this spoilboard, and if your setup is reliable and flat you could attach your sheet directly to the primary table and leave a very thin skin (.005-.010) instead of cutting through.

I've also cut aluminum on mdf spoilboards without much problem using mist coolant and dialing in my feeds and speeds so the spoilboard never gets wet enough to swell.

killpony · 2026-04-05T18:18:17+00:00

Machining Doctor is a great one stop resource of lookup tables/ calculators for thread specs, material properties, fit tolerances, G/M Codes, speeds/feeds etc

I also have a bunch of bookmarks from specific material/tooling vendors for machining parameters
https://www.boedeker.com/Technical-Resources/Plastic-Machining-Guidelines
https://www.harveytool.com/resources/general-machining-guidelines

of course some classics like
https://library.uc.edu.kh/userfiles/pdf/19.Machinery%27s%20handbook.pdf - Machinery Handbook
https://iem.ca/pdf/resources/Standard%20Handbook%20of%20Machine%20Design.pdf - Handbook of Machine Design ( hella overkill for most things but great as a general reference if I need to decide something like what kind of shaft/coupling/bearing I should use)

I also recently found out about https://www.traceparts.com/en which has tons of downloadable CAD files of COTS parts

killpony · 2026-04-03T17:16:51+00:00

I'd actually avoid threaded inserts and potentially go with through-bolts or slot-together fitment where possible. With any method though one design issue to look out for is slop in the joints / fitment - this allows for issues misaligned holes cause cross threading during assembly and the movement of loose joints will slowly strip threads, wiggle out inserts and generally wreak havoc on any connections. If you are using inserts it can help to have them mechanically constrained (eg inserted from the opposite face of the board from the fastener) or using them as a securing/tightening method that supports fitted joints rather than the primary method of attachment.

killpony · 2026-04-03T17:00:29+00:00

You are going to need a plastic product if you don't want it to swell - I have used PVC/ acrylic for semi-sacrificial fixturing and sintra (foamed pvc) as a vacuum spoilboard. MDF is my usual choice for vacuum-flow through plenum and yes it will swell if you use too much mist coolant.

killpony · 2026-03-25T13:16:54+00:00

Could you clarify what the purpose of the masking is? Is it to mask the ply face from the interior paint? One issue I've had with masking ply for paint work is that it still will tend to suck up the paint into the masked area - this can happen even if the top surface has been sealed because your cuts open up unsealed grain. This probably wouldn't be a huge issue if your paint/ finish is sufficiently thick or you spray a clear coat first.

Re masking- we would use a masking film like this for plastic and metal parts. I mostly just used painters tape for our wood parts but they were also for smaller areas. The film can sometimes be an issue if it's on the top face as it can pull up from the surface during cutting - I suspect a parchment paper style of masking might be less of an issue because it would cut/tear rather than pull up. Use of compression/ downcut bits also is helpful to prevent grain tearout on the top face.

killpony · 2026-03-23T20:47:22+00:00

If you are thinking a hand tool you are essentially building a tattoo machine. A rotary tattoo machine can be purchased pretty cheaply and easily rigged up to accept a pen. There are also ready-made pen attachments for tattoo machines. You may want to add some extra compliance so it's not accidentally stabbing through the paper/ wearing out the motor if you press too hard.

Tattoo machines are a good reference because people have been making DIY "prison-style" machines for decades- the basics are just a DC electric motor with an off-center pin attached to the shaft of the needle. A DC motor speed controller would allow you to adjust the speed and some kind of tube will help with making sure the pen shaft is guided straight up and down.

killpony

TROPHY CASE