I was really excited about the Glowforge until I saw this in their faq:
“Does Glowforge need a wifi connection?
Yes, many of the coolest features of Glowforge are possible because we are running software in servers hosted in Google’s data centers.”
I have always had a healthy skepticism towards cloud dependent devices. They are popular with venture capital guys because they create an ongoing revenue stream but create concerns in my mind regarding privacy, security of intellectual property, and longevity/dependance.
The Revolv hub’s irresponsible abandonment by Nest (Google!) is a good example. The Revolv was an expensive IOT hub. When Nest acquired the manufacturer, it was because they wanted the human resources they had, not the product. It is one thing for Nest to abandon further development of the product, but quite another to shut down the servers that made this cloud based product work, and that is what Nest has done.
From a PCWorld article: “As of May 15, 2016, Revolv service will no longer be available. The Revolv app won’t open and the hub won’t work,” the company said on its site. All Revolv data will be deleted.
Nest (Google, er, Alphabet) could well afford to keep a server running to support this product, at least for now. At the very least they could open source the product so the community could keep the service alive. They simply appear not to care about screwing Revolv owners.
That is why I avoid cloud based products like the plague. Clouds are made up of nothing but vapor and dust. “The cloud” is no more substantial than clouds.
I did this today with my Dremel. Holy cow I didn’t realize how tough it would be to cut through! I wouldn’t want to do that very often and absolutely would never want to do it with a hacksaw. No. Way.
BTW, so far (including hacking off half an inch of the Onsrud cutter) I’ve been able to get my time to under an hour for the job that was previously taking ~3 hours in all. I already know of more things I’ll do on the next run that should get me down to ~40 minutes.
I’m now using a Onsrud 63-701 instead of the 63-751. The 63-701 is chewing through this acrylic like nobody’s business so I think I could push it just a little more. I’m keeping my deflection under .0005 knowing that the Nomad can’t do better than .001.
I really appreciate everyone’s additions to this thread. You have all been very helpful for this noob (me).
I did this today with my Dremel. Holy cow I didn’t realize how tough it would be to cut through! I wouldn’t want to do that very often and absolutely would never want to do it with a hacksaw. No. Way.
I. Did. Warn. You.
Seriously, machine steel rivals armor steel in toughness.
BTW, so far (including hacking off half an inch of the Onsrud cutter) I’ve been able to get my time to under an hour for the job that was previously taking ~3 hours in all. I already know of more things I’ll do on the next run that should get me down to ~40 minutes.
Excellent! You’re on the way! With increasing experience you’ll be able to select machine tools and set feeds and speeds very close to optimally on the first try.
I should warn you, however. Tuning machining can become an obsession. At some point, you’ve got to walk away and say this is good enough.
I’m now using a Onsrud 63-701 instead of the 63-751. The 63-701 is chewing through this acrylic like nobody’s business so I think I could push it just a little more. I’m keeping my deflection under .0005 knowing that the Nomad can’t do better than .001.
As I’ve said many times, Onsrud end mills are a work of art. Worth every penny.
Acrylic is a funny one. Some call it hard, others soft… or softish. You’ve obvious got the right tool fo the job and hard it is.
mark
P.S.
Onsrud machine tools are expensive so be sure to carefully put them away in their containers when done. Don’t let anything mar the artwork!
It doesn’t sound like it, but if you’re still having holding problems, have you thought about milling out 60-70% of a row of them. Then using a long shallow clamp, or multiple clamps to hold part of the already cut section of the parts down, and then cutting out the rest? You’d lose a little time due to loading a second file, but you’d likely save time by being able to cut out a row of them at a time.
Someone with more experience I’m sure could fine tune the details, but I think the overall concept could work?
Second thought. why not do this process through mold making? It’d cost you some money for a vacuum chamber. but you could do whole sheets of them at a time. A vacuum chamber is far less than a laser cutter as well. Also each part would take longer depending on your set times, but it is all idle time that could be spent doing something else? I haven’t done the research on the numbers, but I’d be surprised if it wasn’t a cheaper route after the negative was made, and you’d only have to mill at single digit speeds once to get those glass edges.
I found a way to get things to hold until the last cutout, it does require three runs though. My pieces have cuts around the entire piece and milling takes place inside as well. They are also so small that no clamping is possible. I’d either need to vacuum hold or do what I’m doing which is hold down with double sided tape (seems to be working now that I’ve tried a few different tapes and methods).
I have thought of this yes, but I’m pretty sure I can’t keep the accuracy within needed limits by doing it this way. We have many of these machines where I work and I’ve talked a bit with the plastics supervisor about methods. He has told me that I would not be able to get the accuracy needed without a lot of experience and more expensive machines. I’m satisfied (at least at this time) with the current method, particularly since I know I can cut my time down a little more even.
I know you’re all set with your hold down system for these jobs, but I wanted to make sure you’d seen this cool custom vacuum spoilboard someone made for their Nomad a while ago:
Love that thing. If the tape approach ends up not working out, maybe you can design something along these lines. Hopefully this will not be necessary, but just in case…
Keep in mind that vacuum hold down for a PCB has the entire area of the PCB for the vacuum to pull on. When one is cutting small pieces from a sheet of stock, vacuum doesn’t do so well - it depends on what “small” is and how much vacuum there is.
I’ve been doing quite a bit of machining on acrylic lately. I don’t know how much useful advice I can give for flat parts (I’ve been focusing more on 3D carving), but for what it’s worth…
If I’m cutting out flat parts with a 1/8" end mill, I hold down the sheet with carpet tape (the kind that came with the Nomad) and take 0.5mm cuts at 10,000rpm and 1200-1500mm/min. Largely that’s because I use the machine in my not-very-soundproof apartment, but it also helps with keeping the work held down. I’ve noticed (from the smell) that deeper cuts heat up the acrylic enough to melt it, but I’m not sure that really matters; it might not be good for the cutter.
Holding down acrylic sheet is tricky. It’s flexible enough that clamping is no good, but rigid enough that as soon as the tape starts to let go, it lets go completely. I believe it helps a lot to make sure that every point is stuck down securely-- I use a bone folder (or a thumbnail) to get good adhesion on the part, with no bubbles, and I make sure the spoilboard is completely free of dust and maybe lightly sand it with 1200 grit before sticking the part.
The good thing about acrylic, though, is that even one small tab will do a lot to hold the part down. If I’m creating the toolpath manually (I use a Rhino script), I’ll arrange it so that I end up with one tab on each part, then just snip all those tabs with the end mill; probably one part in ten comes unstuck at that point, but the cutter has already moved on so it’s not a problem.
I usually finish the cut surfaces by flame polishing-- just run the hot part of a blowtorch flame over it (in a ventilated area), and you get a nice gloss finish in a couple of seconds. It’s a lot easier than a vapor bath, though I don’t know how it will affect your tolerances. I’d guess it puts a < 0.1mm radius on sharp corners. It’s fun, anyway.
ETA: to remove the tape, I just dump all the parts in the sink, clean off the residue with a drop of paint thinner, and wash the parts with dish detergent and water.
I am actually in the middle of making my own vacuum hold down system. I’ll post a new thread with more info shortly, but it all seems to be coming together rather nicely. First few plenum cuts have gone well. Currently I’m working on a vacuum pump design that will maintain 24" to 27"Hg without constantly running the pump (hopefully quieter milling).
I am actually in the middle of making my own vacuum hold down system. I’ll post a new thread with more info shortly, but it all seems to be coming together rather nicely. First few plenum cuts have gone well.
I’d love to see this… especially if there is a nice way to integrate it into the enclosure so that the vacuum tubing isn’t problematic (not getting in the way).
We set this up by placing 1" MDF on the bed, machining it flat and then creating channels through it… pretty standard.
I saw one design that combined a vacuum bed with T-Rails. One could clamp or vacuum.
Currently I’m working on a vacuum pump design that will maintain 24" to 27" Hg
That’s a nice vacuum! The lower the better! Adjustable?
without constantly running the pump (hopefully quieter milling).
The vacuum beds I’ve used are NOISY, like need hearing protection NOISY. Anything you can do to solve the noise problem will be welcome. The small size of the Nomad would make “vacuum storage” easier than a 5x10 foot monster CNC.
A good vacuum bed is very useful for many types of work. The vacuum has to cause enough force to be applied to the object being cut to prevent it from moving. That means that at some point, a small object is not going to stay put with the vacuum.
I’m running into an accuracy issue that I’m banging my head against the desk trying to figure out. I have several holes in a part that must be 4.8 mm in diameter. If I run a sheet I get 4.8 mm one time and maybe 4.7 mm the next time. The variance is dead on .1 mm from job to job, but granted I haven’t done dozens yet so my sample size is low.
0.1 mm should certainly be within the tolerance of the Nomad. My only guess at this point is shifting of the double sided tape. I’m going to try some Nitto tape on the next run but just by feeling the stuff I don’t think it will be as good as what I was using. Definitely less ‘grippy.’
I did gain some accuracy by running the job at a shallower depth. I’m currently running my passes at 0.50 mm per pass to avoid the shifting issue. I’m hesitant to cut it more than that just because of the time it takes.
Should I trust G-Wizard’s deflection calculator enough to reduce my depth per pass even more but on the flip side increase the speed? I feel like even though the depth of pass is shallower, increasing the feed rate would cause more shifting of the stock than running a slower but deeper pass.
Do I have it wrong? BTW, the product I get back when it is dead on 4.8 mm for the hole sizes is absolutely beautiful. Perfect glass like vertical walls with extremely hard to see tool marks right out of the machine. I just can’t understand how one run can be dead on and the next be off by as much as 0.10 mm when using the same type of double sided tape, processes, etc.
Anyone have any helpful tips they would like to pass on? Thanks in advance!!
0.1mm is ~0.004". You’re beginning to approach the limit of the Nomad. That said, the Nomad is better than that.
At these levels, just about everything comes into play or needs to be though about.
The same G-Code each time? The same batch of stock? End mill? Was the spoiler board machined flat? Same batch of tape? Same process to apply/remove? Double check things?
The Nomad and G code has no idea there is stock there. The commands are just run. Not likely they are the issue. That things are sometimes “spot on” agree with this and also that G-Wizard is giving good advise.
Tape will work when the “sticking force” per unit area times the area being held is above forces applied. Small pieces have less area and so are held less well. Moving slower or using less depth reduces the forces on the piece.
From the picture I’ve seen I can’t get an accurate sense of the scale (no ruler next to it) but it looks fairly small to me (also because I expect LEGO pieces to be small). Small enough that I suspect the piece is moving, not the stock.
With small parts one needs better tape, to seek a different fixturing method, or a different machining method.
I’m not a big tape booster. I come up with other fixtures but when I’ve been forced to use tape 3M (Scotch brand) #410M is what has worked for me. Admittedly the parts may not have been that small.
Can you edit you posting wth the picture of the part with a picture with a ruler in the picture where the scale can be seen please?
Do you clean the stock before applying that tape? The spoiler board?
The hole size in the photo I provided is 4.8 mm in diameter, that should give you a rough scale. My production piece is slightly larger but essentially the same design. Machinability wouldn’t have changed. The problem with other methods of holding things down on the table is that I have (at most) ~6 mm of surface area that isn’t being milled and on average the space is closer to 4 mm connected. We’re talking LEGO scale here so if you have a LEGO anything laying around, you can get a quick sense of scale just by looking at the knob size.
Same G-Code
Same batch of stock sort of…same manufacturer but different colors. Cast acrylic varies in thickness a little from one sheet to the next, but I don’t think it matters at this point. I ran one job with a depth of 2.72 mm and the next batch had the same depth (2.72 mm) and got the .1 mm difference. LxW dimensions were exactly the same as was placement on the table.
Spoiler board was machined flat but I don’t machine it between each run since I’m only running these, the tape comes off of the table without residue and I’m never cutting past the backing paper on the acrylic
Same exact process. I’m actually using a little acrylic finisher before starting passes 2 and 3. I found this helps the cut a little and polishes as it goes along…no buffing afterwards is needed.
I’ve double and triple checked until my head is spinning!
I’ll see what the Nitto tape does and will look into the 3M #410M stuff that you mentioned. I’m so close on this I can taste it, but I just need to get the accuracy down a little closer. It keeps getting better as I try new things and gain more experience, but I feel as if I hit a brick wall with this last mile.
I’ve double and triple checked until my head is spinning!
I understand your frustration. You’re learning and pushing the edge of the envelope.
Spoiler board was machined flat
Just checking… Necessary for edge of the envelope machining.
If that’s 4.8 mm, that’s a small part to be depend on tape to hold AND one wants to machine in reasonable time.
There is a type of fixture that is used for this situation and for life of me I cannot find it… Essentially, it’s a set of adjustable springs that push down onto the stock and the gantry moves up and down. With some felt on the bottom - to maintain your surface finish - it would apply pressure on the tiny part, pushing into the tape.
Tape is the best solution I can come up. My only potential causes that I can come up is the stock moving but I have no clue if it is moving above the acrylic backing, below it (double sided tape side), or maybe a little bit of both. I could probably diminish this a little by slowing the job down again. I did get close to 100% accuracy in earlier experiments, but I think I was cutting 0.25 mm per pass. That takes forever! I could go back to doing that, but I would want to compensate with a higher feed rate…which in my mind would be worse on a stock moving situation.
Better tape is another solution however this assumes one can find it and that it will work with such a small part.
FOUND IT! It’s called a “pressure foot”.
With a bit of thought a derivative of this can machined on the Nomad. Nothing like using a machine to make a machine. The bottom piece I would use Delrin - a super slippery one - or maybe Teflon. Even so I would consider felt or soft cloth to protect some finish.
Definitely worth thinking about 3D printing the bottom part. Material choice is a bit issue.
This works with sheet goods - not much 3D - and provides localized pressure on the part.
I’m busy right now but designing and machining one isn’t too big a project. I could help with the design and machining. The only real challenge is how to attach this to the Nomad. I not in front of mine so I need to stare at it for a bit… already have some simple ideas though.
@mbellon I’m having a hard time figuring out how this wouldn’t inflict some minor movement of the stock underneath. If it has enough pressure to hold the part down then how is that pressure not being forced in another direction (outward)?
Also, would you mind educating me on which is better in terms of accuracy: faster feed and smaller depth per pass or slower feed but greater depth per pass?
@mbellon I’m having a hard time figuring out how this wouldn’t inflict some minor movement of the stock underneath. If it has enough pressure to hold the part down then how is that pressure not being forced in another direction (outward)?
The idea - I’ve not used this device myself - is that the pressure is directed downwards. There still is tape. Between the two it prevents things from moving. You’re free to speak the vendor and ask them about it.
Which is better in terms of accuracy: faster feed and smaller depth per pass or slower feed but greater depth per pass?
In this instance I guess specific to this thread where the part is moving ever so slightly, but I’m curious as to what the rule of thumb is in general.
In this instance I guess specific to this thread where the part is moving ever so slightly, but I’m curious as to what the rule of thumb is in general.
I posted an article, above and repeated here, that explains the general case:
Climb to rough, conventional to finish is the usual choice. Forces parallel to your motion as much as possible. Don’t push into the part.
Use the optimal feed and speed for the end mill and stock, ensure deflection is minimal.
In your case, there are many unknowns. If the part is moving, one would like to move as little as possible. If one goes too slow, one isn’t cutting - making a mess. Too fast, and finish can be ruined.
As you’ve observed, shallower - less bite - serves you better but the time goes way up. I’m not convinced that there isn’t a solution that is between the extremes that happens to minimize vibration and movement… I don’t know a simple solution except to experiment (under these circumstances).
In micro machining - where everything is vibrating like crazy - one just has to go very, very slow to get their part. You need overall production speed. It tape doesn’t work, we need to go to advanced fixturing (the pressure foot is one example but I can think of many others).
Fixturing will depend on how you’re cutting the parts - how many at a time? Can we move them around?
