RC10Nick

iTrader: (9)

I spent the last few days tweaking my tire design and printing out a new mold. I wanted to reduced the outer diameter, give the tire a more rounded profile, and make it a little bit wider. This morning I de-molded my "seasoning" tire and had my first chance to evaluate the new design in my hands. I'm a little disappointed, honestly. The OD and width changes are what I wanted, but the profile seems too rounded now, and the treads don't go as far to the edge of the tire as I'd like. I took this comparison picture to show what I'm talking about. The tire on the left is the latest design, the middle is a JC DDv2, and the right is my first design. So while I've made a step in the right direction, I think I want to tweak the tire shape a little more. This time, though, I think I'll print the tire itself before I print the molds. The molds take me about 3 days to print so I'd rather not do that unless I'm sure I've got the design exactly the way I want it. In hindsight it's easy to see that's what I should have been doing, but I don't' think you can blame me for getting excited and wanting to go straight to making tires.

silvertriple

Is there any retractation to consider when building the mould?
On my side... designed a mould for Shogun tires based on what I learned from you and from the people of Loisirs Creations RC, and started print tests. Unfortunately, the print of the first part failed mid print with a nozzle clogged... Need to fix this first, before proceeding to next steps...

RC10Nick

iTrader: (9)

I use whatever the Cura defaults are for retraction settings. I've never really messed with them. Good luck figuring out your clogged nozzle problem. It's always a headache when the printer itself is the problem.

silvertriple

Well, when speaking about retractation, I was more thinking about the PU resin during the cure time... but looking at your answer, I know I have probably overthought about this
And yes, my printer is a headhache, which doesn't really help to get to the point I can test something :-/

RC10Nick

iTrader: (9)

Oh, do you mean the resin shrinking as it cures? The data sheet for the smooth-on stuff I use has a spec for shrinkage. It's something like a few thousandths of an in per inch. So a 1 inch long part may shrink about .002 to .005 inches when it cures. It's not something I've had to worry about as its so negligible it's basically non-existent for my purposes.

RogueIV

iTrader: (5)

To be honest the tread not being on the very edge might help in situations where you have issues traction rolling on high bite surfaces.I mean a lot of people end up shaving the outside nubs anyway depending on conditions.

silvertriple

Printer is back online, and my tests can resume... I reset all cura parameters to default and set a temp tower to reconfirm the temperature... Which is exactly what was set before. The retraction is now different and bubbles no more (maybe the clogging issue was coming from this).

Today's printing test has two objectives: confirm lettering would work. I'm printing this test in 0.2mm per layer. There should be a way to do better than this... And it should work.


Next objective is to make sure spikes can print properly as there is bridges and no support, and this will be the difficulty.

The first row of spikes seems perfect, even on the bridged part...


on the second row the overhangs are harder... A few degree of angle can change a lot. That being said: I've not done a single cooling optimisation yet on the printer and all is set to default. I have in mind he fact I want to change the extruder by a direct drive extruder and improve the cooling... But for the first test, it is not really bad.

I will print the full mould over the week-end. This is good progress and also good insights for other moulds which should be much easier to print than this one...

RC10Nick

iTrader: (9)

That's looking pretty good Marc! The print quality definitely looks better than what my printer can do. I'm excited to see how everything works for you.

As for my own tires, I got to run them on dirt for the first time today! They were... not great if I'm honest. The ~40A rubber feels like the right compound for the track, but I think the tall profile and the very soft open cell insert resulted in a tire that was just too squishy. I picked up a set of closed cell inserts at the shop and I think those combined with the redesigned tire carcass should really get them in the ballpark.

*edit*

So I was looking at my tires and noticed the color seemed different. Even on the one tire I brought but didn't run at all the color looked - less vibrantly blue. Turns out I was right, check this out:


This tire didn't touch the track at all (obviously, it's not even mounted). But it did sit out in the sun for a good portion of the day on my table. I also think the UV exposure is causing the rubber to break down and off-gas something. I kept noticing an awful smell throughout the day at the track. I just thought it was something rotting in the trash somewhere. No, turns out that smell was the tires. All 3 of them smell disgusting, even after sitting in my basement for several hours after getting home. I have a headache and some nausea tonight and I suspect it might be due to the tires (or possibly I didn't eat enough dinner, idk getting older sucks). Smooth-On does sell a UV stabilizer but the technical data even says that a fully UV stable polyurethane resin isn't possible. They also sell UV stable pigments but don't say if the pigments also stabilize the rubber or just prevent color fade.

Tomorrow I'm going to place a bunch of tires out in the sun to see what happens to them. This is interesting and something totally unexpected.

2wdMod

iTrader: (42)

More great info for the masses Nick.. Thanks again for being the lead guinea pig in this endeavor! I have a bit more info myself.. I have established the complete cure time for the silicones I am using for the 1/24 and 1/36 cars is around 30 days.. The compound feel finally stabilizes at that point I have found.. traction seems slightly improved . I am assuming due to less side wall squirm..

RC10Nick

iTrader: (9)

Results from all day UV exposure - there seems to be a correlation between shore rating and odor. The tire made using VF60 and softened to 40A with the SFII and the Flex-It 40 both had the strongest smell. They're in the trash - I just couldn't stand the odor any more. The two tires that were purely VF60 smell some but not as strongly. One was black and one was blue and I think the black tire's odor wasn't as strong.

All but the black tire had visibly changed color.

I'll have to try making some black tires in the softer compound. The black is a fully opaque pigment vs the blue being slightly transparent so I suspect it might limit the UV damage to just the outermost part of the tire while the blue might let the UV penetrate deeper into the rubber.

silvertriple

RC10Nick , while looking for Vytaflex 60 here as I need to supply some for my own tire project, I found there was a product from the same provider call Sun Devil
"Permanent UV stability in liquid urethane products is not possible. Ultimately, the only option is to delay the degrading effects (color change and surface break down) of ultraviolet light on these materials. Sun Devil™ is a one component liquid additive that will slow color change and physical degradation due to UV exposure for many Smooth-On liquid urethane products. Sun Devil™ is added by weight (gram scale required) to the urethane rubber, plastic or foam system. Results will vary and will depend on intensity and duration of exposure to UV light to the cured material over time."
May be I should also consider this...

RC10Nick

iTrader: (9)

Marc - I found the same thing. It looks pricy compared to the volume of product you get but since you only use 1% by volume of your resin it should last quite a while. I mixed up another tire last night and I'd have only used 0.5g of the stuff.

So aside from the whole UV resistance detour, I noticed the tires I tested on Saturday behaved completely different on the track when it was wet vs dry. On a dry track it was pretty loose and unstable, but on a wet track they were much more planted (though still not as much as the DD's, but there was certainly less of a gap). I think this coincides with something I've known but but never really thought about in terms of how it applies to my tires - on track surfaces where the pins can "dig" into the surface you get more traction from the pins, but on hard track surfaces the decreased surface area contact you get with pins reduces tractions. I also think another reason my tires didn't do so great when the track was dry is because the pins themselves are completely unsupported and can easily fold over. I've noticed lots of other popular pin style tires aren't 100% small pins, lots of them have some kind longer bar in the middle of the tire. I think those bars do two important things - increase the tire contact patch and prevent the tread from folding over. Another thing I noticed on Saturday is lots of guys were running bar style tires. Now that I think about it it makes sense - the track was hard and dry but not too dusty so a tire with a connected bar pattern (like a JC Ellipse) would have lots of surface area contact with the track and the bar pattern is fully supported which means no chance to fold over. So with all of that in mind I've tweaked my tires to add in some longer bars between the pins. Check it out:



I think this tire will work much better on the hard/dry track surface. I've started printing the first mold piece this morning and I expect by Friday I'll have my first tire made from it.

Other odds and ends: I've seen DIY recipes for a mold release that is nothing more than petroleum jelly mixed with mineral spirits. I want to give this a try as my bottle of spray on mold release is close to running out and I'd rather dunk the mold pieces in a bath of mold release as I think that will get better coverage on mold. I'll have to mix some up to test on one of my Mini-B molds to see how it works.

RC10Nick

iTrader: (9)

Quick update, now it seems as I'm the one having printer problems! The last three prints I've tried have all failed with a clogged nozzle about 3 hours into the print. I've completely disassembled and cleaned my hot end and swapped a new nozzle on so here's hoping that's fixed. No way I'll have a tire with the new tread made by tomorrow, I don't even have a single piece of the mold printed yet.

The mixture of petroleum jelly and mineral spirits seems to have worked pretty well as a mold release. I applied it with an acid brush and wiped up all the excess with a paper towel. I like that I don't have to spray anything now but I do have to be careful I don't leave too much of the mixture in any of the tread pockets in the mold because it will prevent resin from going into the treads.

This Saturday is another race at the dirt track and the weather is looking good. I have two more tires molded and glued up with closed cell inserts. I used the mold from last week that has the smaller profile and is slightly more rounded than I want. A quick run on my basement track tells me the lower profile and the closed cell inserts have fixed that squirmy feeling I mentioned with the original tire design so I'm excited to try them at the track.

Finally, the rubber of the two tires I made this week feels pretty different than the last batch and I know exactly why - I was using months old VytaFlex 60 up until now. It was definitely at the end of its shelf life and maybe even past it. The rubber from the brand new Vytaflex 60 feels a little firmer but also a little grippier. I think I'll get something like this to help preserve my resins so I don't run into this issue again:

silvertriple

Last times I did have that happening, it was due to the lack of contact between the nozzle and the bowden tube on my Ender 5 Plus... Changing the nozzle was not enough : the tube was not seated correctly : had to recut the tube, put it in contact, torque the nozzle, and then torque the pneu fit... Until next issue. Basically if the nozzle is clogged more than once, I would do the full procedure... Can particularly happen if the nozzle got hot without filament (because filament runout sensor is dead or not present)...

2wdMod

iTrader: (42)

also double check hot end fan.. I had one that was going bad and was only spinning at about half speed with no noise. Shorter prints were no issue, but I was getting clogs from heat creep on the longer prints. Rebuilt the hot end a couple times before I realized what the issue was.