Reply To: Can an aluminium shooting board guide rail abrade the edge of a shooting plane?
Ever so many thanks Larry!
Your reply helped a lot. I ran the piece through the thicknesser, after first resawing it on a table saw. Both worked very well; only the very needed extractor got its hose clogged up by the chips – well, they were more like shavings rolled together into narrow straws. Nothing to it but to do without the extractor. Thankfully, this activity didn’t take place in the workshop, but in what was once a cowshed, at a beneficial temperature of just above freezing.
Working with the acetal plastic has been quite pleasant, while at the same time really intimidating. You mentioned ebony; my thoughts have been on bog oak. There’s no texture, it is homogenously black, and it will be very difficult to get a new piece, should failure be the outcome. Even cutting off a test piece felt a bit.
I used a 5 mm brad point and a 6 mm thread. The flat head screw went down as if through a metal thread, but there never was a really distinct stop to turning. Supposedly, that means that I should use longest screws possible, several of them, and stick to the flat heads?
When I mentioned an extractor I was thinking 4” or larger pipe, but the shavings can still wrap around the impeller in a single stage unit. The shed was a good idea.
Here is a screw head guide I picked at random.
https://www.fastenersuperstore.com/fastener-guides/screws-head-styles
Flat head in the USA means a screw that presents a flat surface that you see and is countersunk, usually at a 82° cone.
I don’t recommend those screws in any plastic with the possible exception of hard nylon or UHMW which will give. Most plastics can develop stress cracks when presented with a wedge.
Any of the fasteners that present a flat surface to the plastic will work, including button head, pan head, cheese head, truss head, etc. you can sink them into the work with a larger hole if they protrude too much.
You might jump up a size in Metric threads. I’m clueless what the options are in Europe. All I see here is 1mm pitch with 6 mm screws. Look into whatever metric pitch is used in cast iron. Here that’s usually 1/4-20, closer to 1.25 mm pitch. You have to jump to 8 mm screws to find that pitch here in metric.
At least use the longest threads that fit and make sure your tap doesn’t bottom out. If you can, drill deep enough that the full length of your screws have fully formed threads. Otherwise you risk stripping them. Consider a nut on the back side, or the sex bolt/Chicago screw/ barrel bolt option.
While it may have felt like aluminum and was originally developed as a easy machiring alternative to aluminum and Zamac (Zinc aluminum, magnesium and copper alloy ), it doesn’t have the shear strength or tensile strength of those metals. The listed shear strength for Delrin is 11K psi and aluminum is 27K psi. zamac is in the 41K range, depending on exact alloy.
Tensile strength is similar. Delrin is around 14K psi and aluminum 31K psi. At 14k psi, it can be compared to Oregon ash or American black Cherry. Most other acetals spec lower, because most are copolymers. It’s like the difference between a single malt and a blended whiskey. 😉
So you might consider going up a size in thread size and/or thread pitch.
If you are just trying to keep the sole of your shooting board down, consider VHB double faced tape instead of screws. 3M makes it.
I guess I lucky here when it comes to finding acetal The largest employer in Oregon is Intel, which has a huge chip plant. They and their subcontractors use literally tons of the stuff for jigs and fixtures. It just takes a few minutes of dumpster diving to get strips for things like shoot boards. They are usually glad to lower their landfill costs.
