Yesterday I was doing a bit of testing regarding threaded holes for 5mm screws in Delrin (aka POM, acetal) and found that a 3/16" drill bit drilled the perfect size hole that when given a slight nudge, a 5mm screw would enter the hole and form its own threads in the plastic along the way. The threads formed in this manner were actually giving me a better, more solid grip than I was achieving through traditional tapping. Well, last night after having spent a couple painstaking hours tapping the ends of all my ox extrusions, I began to wonder why I hadn't tried the earlier experiment on aluminum. To make a long story short, it not only worked, it worked exceedingly well and had I considered it sooner I could have reduced a couple hours of hand tapping to just a few minutes of drilling. The grip on the screws was firm and tight and while it loosened a slight bit after a few rounds of threading/unthreading it still felt tighter than the hand tapped holes. An attempt at levering out the screw was unsuccessful but with 14mm of the screw embedded in the hole this result was pretty much expected. If you've got a lot of holes to thread whether they be deep load bearing holes or shallow end cap holes, you might give this method some consideration. I know my M5 tap won't ever see the light of day again. _______________ Conditions of the experiment: 3/16" Dewalt titanium coated bit in battery powered hand drill, Tap Magic cutting fluid, black 20x40 extrusion. Disclaimer/Safety Recommendations: Your mileage may vary. Always test first using non-critical parts. Use a cutting fluid or oil to reduce wear on cutting tools. Always wear safety glasses. _______________ Update 4/16/15 For screws gripping into delrin (pom) 11/64" (0.1719" or 4.37mm) seems to have the best grip. For screws gripping into aluminum plate, #14 wire gauge bits (0.1820" or 4.62mm) seem to get the best grip and reusability. Threading oil was helpful. For screws where grip is not important like end caps, 3/16" (0.1875" or 4.76mm) holes are more than adequate. Where grip is important, use screws long enough to get at least 10-12mm threaded embedment.
Thanks for starting a new thread. It saves sooo much time when I'm trying to find it again!! I think I'm going to find that really useful!! Perhaps you could put a copy of this thread in to the Useful Tools Area? Gray
Makes sense. A 4.2mm tap drill is recommended for an M5 x.8 formed thread. https://www.google.com/search?q=for...aa87aaf17b4d961af2d%3FC%3DD%3BO%3DA;1275;1650 Their about the same size. The 4.2mm looks a little tighter than the 3/16 though.
Actually, 4.2mm is for cut threads. For formed threads 4.6mm is recommended. And if I had one, I'd give it a try but as these screws don't have a pointed tip like a forming tap I really question if they will go into a 4.6mm hole.
Typo. That's the chart I was referencing. Your probably right in that the flat top won't be as happy in the .181 hole vs. The 3/16.
I ended up using self tapping screws for my build instead of tapping for M5 screws. Saved a bunch of time, and didn't have to predrill or anything. Just used the existing holes in the extrusions! Very solid, even with repeated screw insertion and removal.
Did you use M5 Self Tapping Screws John? Anything else you can suggest on this topic would be greatly appreciated.
I used the self tapping screws from the open builds parts store - Self Tapping Screw I did run out at some point, and found the same screws at my local Ace Hardware. Easy peasy!
I looked at the Self Tapping Screws from the Open Builds Store, but the person who I purchased my Ox Router Plates from used 1/4" Aluminum for the X-Gantry Outer Plates and 3/4" length screws just weren't going to give me a satisfactory hold strength. I tried using a 3/16" Clearance Drill and everything is Kosher now. Also thank you very much to everyone for there immediate and knowledgeable responses.
just starting my build and this 3/16" drill vs tapping will save hours! THANK YOU!!! After trying it on the main rails: Too easy to strip... ended up using #10 self threading screws... Probably will go with tapping...
