Tin Can
I’m always open to suggestions. For this particular application I don’t need precision but there are a few other things I’ve worked on that do require relatively fine tolerances and I don’t want to do them by hand anymore.
Originally Posted by Havoc
I have made project parts from 3mm and 5mm styrene sheets and it is very easy to cut by hand with a saw (fine full-size hacksaw or coarse jewellers saw, depending on the part) rather than a knife. It obviously depends on the size of the item though, as a part several feet long would be awkward to cut and finish, so I suppose that is the sort of thing you mean. My largest stuff has only been up to about 200mm long by 120mm wide and, with hand finishing, precision is better than 0,25mm (1/16" is about 1,6mm). Probably a small bandsaw, a slow cutting-speed and some simple jigs would be the ideal solution?
No, not Brother hobby cutters. 1/8 inch Styrene is hard and stiff, and not like soft vinyl. And for solvent welding you need clean square edge but preferably with a tiny bit of tooth; lasers are not going to give you that without some post-sanding.
Now how do I personally do it? No, not with a hacksaw blade attached at one end to a flexible willow stick and to a wagging hound dog tail at the other. In the past I had a customized horizontal cutting table with a special small high RPM circular saw (not a toy by any means), and a specialized blade of the type used for airline honeycomb aluminum panels, so capable of handling all kinds of plastics too, and even plastic-aluminum sandwiched composites.
Then I switched over to my big wall-mounted dual-rail Fletcher scoring and knife machine, which is useful for all kinds of thicker darkroom materials like fomeboard too. The plastics scorer trims the material to size nicely; but I still have to precisely smooth and square the edges for sake of solvent welding using a laminate trimming bit on the router table. That certainly worked well enough for all my slot-style print washers.
Now I'm most likely to use my Festool rail saw with appropriate plastics blade, atop my tricked-out Festool shop table. This has excellent dust control due to the integral vacuum system. Won't say what I paid (or didn't pay), since I set up the main dealership in this half of the country and was given an incentive to know what I was doing. But today, you might pay about 3K for that kind of setup. It works so well that no post-edging or sanding on a router table is even needed. Doing small pieces is tricky unless you make appropriate jigs.
But if I were in Michaels shoes, I'd do precise strip cuts on the Festool table, then size those down into all the little sections using a very nice small Makita Japanese-mfg power mitre saw (no longer made) with its precision stop system. Their own current bait and switch Chinese made equivalent is probably around $250. The last of the actual Japanese ones (designed at my request, incidentally) went for around $1000 at the bitter end, but only around $375 originally. The Fukushima disaster changed everything when it causes energy prices to soar in Japan. That was the demise of the former Japanese miniature circular saw model too.
Drew, wouldn’t all those power cutting options simply melt the styrene?
No - exactly the opposite, Michael. It's precisely what professional sign companies prefer for even delicate brittle plastics, as well as honeycomb aluminum panel specialists, an even fussier application. Some have even switched over from hundred thousand dollar panel saws to this kind of portable gear. You need to recognize that it is not like the regular kind of Cheapo Depot circular saw you see carpenter's casually working with, though they'd get quite a few tasks done more efficiently if they did. And using the correct blade is equally important.
But unless you have multiple uses for this kind of gear, it is a bit of a stiff investment. One compromise you could realistically make
is to get the Plastics shop to cut your material into consistent linear strips, then just size it down sectionally using a good mitre saw with a sizing stop and clamping system - maybe a $400 investment, not including any vac dust extraction gear - gotta be careful about that - certain kinds of dust including plastic can generate a lot of static and potentially turn an ordinary shop vac into a little Chernobyl incident. Seen it happen. But fine light plastic dust flying all around onto everything isn't fun either.
I don't know your comfort level with power equipment. The kind I've described is safer and quieter than most, but still one should inventory their fingers both before and after use. Even the safest power tools aren't foolproof; and even I don't personally use mine if I'm not alert. Correct technique alleviates almost all the risk, so it's important to learn from something better than most web videos, which often seem like they were designed for slicing off mass spare body parts for Frankenstein monster builders, so dangerously stupid are some of them! The actual Festool site has appropriate instructional downloads.
There is a specific Festool accessory jig made specifically for repetitive precise strip cuts with their rail saw. But there's a distinct learning curve to any of this.
Last edited by Drew Wiley; 25-Oct-2021 at 16:55.
...and now the next problem with this. I need a few plastic gears. Not anything high-load or high precision. But they have to be resistant to typical black and white chemicals. Seems like it should be easy but for some reason not. I can't really find any that are made of the typical darkroom plastics (HDPE, HIPS styrene, PVC, ABS etc.). They seem to mostly be various types of Acetal (Delrin for example) and Nylon. Understandable I guess since these are better for moving parts, although they absorb a lot more water than styrene.
Any ideas? Sources? I've looked at a few places like NHK and SDP-SI.
I wonder if I could get away with the commonly used Acetal M90-44 ("Duracon"?). It would only ever really be exposed to weak/dilute acids/bases and salt solutions, and not for ridiculously long periods of time - just film processing.
Worst case maybe I can use Lego (ABS)?
Or perhaps I should use stainless steel gears.
I think that probably much can depend on local management. But, I've built many projects with the indispensable help of Tap Plastics in Portland, OR, and I've always been very satisfied.
For the volume of work that they do, I don't think that 1/16" tolerance is too bad. Usually, if a dimension is that critical, it's because I have to have two pieces with exactly the same dimension. In that case, I will ask them to cut both pieces at the same time. Or, I might have them cut a piece 1/16th" over, and then narrow it to exact dimensions with a belt sander that I have.
It's rare that I have to return a second time for my cuts. As long as I explain which cuts are critical, they do their best right then to keep them accurate.
Any skilled small cabinet maker could be hired to do this very precisely, especially if you offered to buy the appropriate circular plastics blade for him, which don't come cheap. But exact dimension isn't as important as sheer consistency of dimension, which Tap should be able to provide once they lock down their settings. Just communicate well in advance and don't be in a rush, so that they can give the project due attention.
Gearing : there are specialty suppliers for this very kind of thing. Do a web search, or try McMaster first. No, you don't want ABS; nobody is likely to make gears out of that anyway unless its some toyish application. You want machinable solvent-resistant Delrin or durable HMW (high molecular weight) nylon, Acetal, or perhaps 316 stainless steel (noisier). At the heading of each catalog section, including their online catalog, McMaster gives good specification comparisons on the various materials. Then you can home in on more thorough solvent resistant specifications of potential candidates looking elsewhere.
For gears, those who serviced processors would have literally buckets of gears from dismantled processors they saved for future repair work, so see who serviced processors/minilabs in your area for sizes you might be able to use...
Steve K
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