Which screws for this project?

If you are trying to resist shear forces, you want the screw as large as possible in diameter and you want to avoid having the threaded portion in contact with the plates in shear.

The bolt strength is not going to be terribly important, the aluminum has a unknown strength but certainly less than half that of the bolt.

My first choice would be a socket head cap screw in black phosphate finish but all of those are fully threaded until you get to over an inch long.

Using a locking nut (Nylock) would be a good idea in this high vibration application.

You didn't ask but I would be look> Note: In order to avoid wasting your time, please be advised that

Yup yup, good thoughts IMO.

Like what, specifically?

I'm very familiar with those and other off-road in-line skates. The Coyotes were a chore to push with, the pneumatic wheels made them very slow for anything but going downhill. There are others, but nothing that resembles the function of mine for rough street skating. I've used 100mm wheel speed skates. Mine are for speed (hard wheels), stability (low profile), and handling bumps (big front wheel). I'm still working on putting a stopgap between at least the first and second wheels, that's what my earlier question about Delrin was for.

Problem with the stopgap is that it needs to absorb shock without moving into the wheels. That's a really tough qualification. I think it's going to be a breakaway type, so that if I hit an extremely hard object with lots of force, it will absorb some of the shock by shattering, then it will be replaced. It would need to be replaced periodically anyway.

I expect the glue to resist the shear forces. The screws are only (hopefully) to temporarily keep the thing from flying apart if the glue fails. Then everything would be remade.

Yes, that sounds desirable, however unlikely.

Yeah, it's general-purpose 6060 or 6061 from McMaster. Once I know what's needed, I would consider going for better aluminum.

I like your idea allot. But I agree super glue is wrong for this. Epoxy is probably good. You should look at 3M or Duro to find out which one. Sanding it wetted with the epoxy is a good idea. I actually like the two mounting points with one being the second axle (first small wheel) the best and epoxy bonding to take most of the load off that little screw up front. Excellent idea though. Karl

wow, thanks

Maybe some Devcon or one of the 3M family. NOT a 5 minute type, you want a longer stronger cure. You would need to look over some of them for bonding abilities. I use a few different types but don't bond aluminum much. I would also do a dry sanding to remove the coatings, then use a finer grit wet paper, whetted with the epoxy just prior to assembly. That would give you the best bond.

carbon fiber reinforced resin? Or maybe some light aluminum with molded delrin material over it? How about machining them out of the molded rubber they make hockey pucks from?

1/16" bar seems awfully light for that - think I'd go with 1/8" at least. While the bar is quite strong in the wide direction, a little side force and it will twist or bend. I'd also extend it back along the frame for a couple of the axle screws - get longer ones and use them to hold the bar on as well.

It may be the perspective, but that big wheel seems as though it might rub on the boot. I don't know a thing about those skates, but wonder if it might make sense to make that wheel higher than the others? That way, it wouldn't interfere with normal skating but would still guide the skates up and over obstacles when you hit them.

6-32 and 8-32 screws seem way too light. I'd use 10 or 12. The skate frame may be adequate to hold the threads, but I'd probably use nuts as well. They are readily available. Loctite on the threads will keep them tight.

John Martin

I know you're asking for screws, but have you ever considered using rivets as a better alternative?

At idle, there is a tiny clearance between the wheel and the boot. I was considering sanding/filing a notch in the very thick plastic boot, but the wheel made a smooth notch by itself. I guess the metal flexes upwards too.

That was my first plan, thinking it would further increase the obstacle surmounting capability of the front end. A competing concern is that the main benefit of an in-line skate with at least three wheels (on the street) is its ability to span small potholes without the front or rear wheel dropping into the hole. The current same-level placement helps the small second wheel roll over obstacles.

For what it's worth, the design complexities of in-line skate wheel size/hardness/placement are more than meets the mortal eye. Much fun.

I did 9 miles this morning. Seems okay so far. Street skating isn't normal anyways.

Thanks to all of the replies.

If you'd ever seen me on roller blades and seen the bike path I was learning on you'd know why I like it. You're welcome. Karl

You might want to consider shoulder screws (bolts) for attaching the wheel plates to the skate frame. The shoulder section eliminates having any threads in the shear area. A suitable washer and nut should/would probably be better than threading a fastener into thin sheet material. Using 2 per plate would not require any adhesive.

There are numerous styles available, and types with low-profile heads are commonly available (less likely to get snagged by some passing object).

WB ......... metalworking projects

You have several issues from what I can see. Use button head screws, a good fastener house will carry them. Your main point of weakness is at the screw location where the torsion will cause stress fractures and weaken the the aluminum. Try to find scrap anodized aluminum and cut out a piece from that. Aluminum will corrode when not anodized. It makes a salt on its surface and will eventually reject the glue and corrode around the fastener from the uneven charges. I would consider a piece of titanium for the plate. Just search on Ebay for titanium sheet, it is MUCH stronger than aluminum and highly corrosion resistant especially for the salts and organics that come from the roadway. It is strong as steel with less than 60% of its density. Search for titanium sheet on Ebay, enter 310062160956 into the search field, it looks like a likely candidate. It is .107" thick which is very strong, which you need as the bending forces on this larger wheel is much higher than the smaller wheels. Think triangle on the bar design. The racking on the frame will crack it over time if twists too much so take the support further back in the frame. Airplanes suffer from this and they only bend a little compared to the twist forces in your current set up. I would secure it in three or four points. Screws top and bottom in the gaps between where the wheels meet and two out on the tip of the frame. This will stiffen the frame considerably. You need a good safety factor on a design like this. If you are going down the road and hit something, it could cause a bend on a stress fracture, which in turn allows the wheel to contact the frame....oops. So a light design that works today, may be a disaster tomorrow.