Casting a Polyurethane Sprocket and Final Track Assembly | Snowcat Build
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- Опубликовано: 8 фев 2025
- We finally have gotten out track grousers back from galvanizing. It's time to get these tracks assembled! We finalize our sprocket design and start 3D printing a test sprocket mold and pour our first polyurethane sprocket! It's awesome! #custom #snowcat
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Try putting holes in the bottom of your mold for ejection pins. Cover the holes with tape when pouring. This way you can reuse the mold.
Good idea!! I actually have made a few changes to dissemble the mold more so I think not having them this time will be okay. But I will keep that in mind on the next parts I make
You also might try adding chopped fiberglass fibers to the resin to add strength to the sprocket. When the fibers lay across each other they strengthen the stucture. They use this technique in injection molding.
Hmm also another very interesting idea! I’ll see how the first sprocket seems that is a great idea to add strength.
Yessssssss...snowcat time. Im happier than a new priest at a boys home.
Hahahaha
@@CenterLineDesigns hey man just finished the video, great job. I was left with a question at the end. Since you increased your track grouser spacing by two, couldn't you / shouldn't you, half the amount of teeth on your sprocket.
Well very interesting. So I did forget to cover that but since we cut them by two I went to an odd tooth sprocket. So instead of having a big blank spot in between but going odd number of teeth a grove only sees a grouse every second rotation. That makes better use of the resin. I wanted to keep the diameter the same because that matched my torque and speed calculations since that’s based on the hydraulic motor.
Good question! I’ll cover that more in a future video!
Essentially the sprocket will wear half as fast as you would expect. Hopefully lol
@@CenterLineDesigns I see, that makes perfect sense. Increasing longevity by halving the wear.
Can’t wait to see how the real one turns out. I think you just saved me a ton of time. I have been looking for a roller that is no longer made for an expensive piece of equipment and I never thought about using my 3D printer to make a mold and then pouring the resin to make the exact size I need.
I can’t wait either. Nice I am so glad that in some way I am helping others out! Good luck if you have any questions feel free to ask
Your sprocket IS on the right track!
lol. Thank you!!!
I laughed when he said tgat
I didn’t hear it until after hahah I laughed too
I would add bolts to the mold on back side and see if your can screw them in to press mold out the opposite side making the mold reusable. I can’t wait to see this in action!
Good point Lloyd. I’ll see how it goes being that the full size it printed in quarter segments it might demold easily allowing the reuse like you say!
You should be able to drill and tap the PLA. But only concern would be stripping out the holes unless you can incapacitate nuts somehow. It maybe something to try. 👍
I do have those melt in nut inserts. However I am thinking now that with the mold being round I man just be able to use heavy elastics to hold it together
I have a old Bombardier that has a similar track, I need some new sprockets so I'm going to try and pour my own now!!
Oh that’s wonderful to hear! I need to learn more about how to adhere it to a metal core for future projects. For this one I went a different route for mounting
@@CenterLineDesignsMaybe cast in metal tee nuts or threaded inserts.
You can get a few disposable syringes and fill them with equal amounts of that cast liquid and inject them in the cup at the same time. Same a little time on the pour
Oh good point. On your point maybe with the full size sprockets I measure each out individually and mix in a third cup. Hmm I’ll have to give this some thought. Thanks!
A major advantage of printing a "positive" to make a mold from is this. If your polyurethane sprockets fit properly, you could take your positive to a machine shop and ask them to make them from the metal of your choice from that pattern.
Well you don’t actually want a metal sprocket. It will wear the track grousers. And with the hundreds of hours of work that went into them I don’t want the wearing out. Using polyurethane is a designed wear point
@@CenterLineDesigns True enough, and a point I realized AFTER I posted my comment! You have to wonder though, how did/do Cat/Deere and Sno-Cat get around that with metal drive sprockets and grousers. . . .
I think in some scenarios like excavators and Dozers they use different grades on metal and design in that one wears more than the other. Don’t get me wrong metal sprockets are 100% a viable option. However the materials and grades of metal I have at my disposal are more limited mainly because my budget is. So I think I have found a balance between designed wear and affordability. Good discussion. So much goes into design ideas
Making progress. Great to see.
Yes! It’s a bit slow but just trying to make sure I don’t make too many mistakes.
Cheers Scott!!
G'day mate awesome work again
Thanks buddy!
This would be the time to have a CNC router! Hopefully the printed mold will be good enough for 2 parts, but as a guy with a router who's also using urethane, I cringe at the idea of 40+ hours for a singlle segment of the mold! I'd recommend making a silicone mold by painting on a "thin" layer of silicone, like 1/2" or so, and then laminating a rigid fiberglass shell over the silicone to hold it's shape. Then it is easy to make multiple parts.
Yea the more I said it, it started to sink in. I think I have a plan to reuse the mold. I agree that’s a lot of hours for them all
A silicon mold would be good for many castings, a little expensive though. vibrate it to bring the air out.
Good point
NICE
Thanks!
"The sprocket is on the right track." Hardey, har..
Hahaha
Those grousers look really nice! Taking a torch across the top of the epoxy. Once you pour it, will get rid of the bubbles. Are you going to be sandwiching the sprocket between metal plates with bolts or are you casting the resin over a metal core?
Good call. Sandwiching between plates. It’s been on my mind but I think it will be good
@CenterLineDesigns sounds like a good plan. They were overmolded on my Tucker but I don't know if that is a simple process or you need a specific technique to bond with metal effectively. You could potentially do both I suppose. I'm taking notes because if I get the chance I'd like to build one myself. That tucker I had when I lived in AK was awesome.
you can add holes to the flange to lock the rubber on.
If it’s a lil flimsy , I wonder if you could impregnate a plate of steel in the middle w the same pattern , it mite slow down any ware if the plate was contacting the track along w the poly 🤷🏼♂️🤷🏼♂️ love the build👌🏼🤘🏼🤘🏼
That is a good idea. I have noticed that over the past 24 hours it’s has gotten harder and considering that it’s only about 1/2” of material it’s crazy strong. So when it’s 2.5” I think it will feel really solid. My confidence has increased from when I demolded it.
I suggested a similar idea about using a three piece design with a steel gear as a core sandwiched in between two slabs of UHMW-PE. I am interested to see how the cast polyurethane gear works. I hope there are no sharp corners where a stress crack can form, all corners need a filet radius as stress relief.
So UHMW was my first idea but after talking with plastic suppliers they said that it’s not the right material. But suggested Nylon however that stuff is expensive. I have a lot of confidence in the polyurethane and I know this is the exact product they use on full size cats!
Your snowcat looks awesome! I have one concern, snowcats typically have a very wide stance for stability and a fairly short overall height to keep the CG as low as possible, are you worried about tipping over as the two tracks are fairly close together widthwise and the cab where people sit if fairly tall meaning your CG is elevate? I wonder if your grouser bars are going to give you enough traction on the snow. Typical grouser bars on cats have vertical pieces of steel protruding perpendicular to the rubber tracks that act like paddles in the snow and give a lot of 'bite' in loose snow. I also think your polyurethane drive sprockets are going to break under the load of driving this heavy machine, consider a three piece sprocket with a steel sprocket shaped core and two machined sheet of UHMW polyethylene that encapsulate the steel sprocket and through bolts keep all three pieces together. The steel is the back bone so you do not break the ring or teeth off and the UHMW plastic is insanely tough, abrasion resistant, and slippery to drive the grouser bars but not chew up the grouser bars.
So I am not worried about tipping. The CG is actually very very low. The cab is light and although it looks big it isn’t heavy. The tracks themselves weigh 400lb each and will aid in keeping the tracks on the ground. I have a lot of confidence in the polyurethane sprockets. 100% polyurethane sprockets are used for full size snowcats. UHMW isn’t the right material to use. I talked with plastic suppliers and they don’t recommend UHMW. If anything they suggest Nylon. But that is very expensive at nearly $1500 each.
I designed the tracks they way they are for many reasons. Big one being maneuverability and also designed to the terrain I have. I don’t get 20’ of snow. So although I call it a snowcat keep in mind it’s a designed for different purposes.
@@CenterLineDesigns I am interested to see how it all works out
Thanks! It’s definitely a learning curve and likely there will be issues but I have put a lot of time into design. So fingers crossed
Don't worry about the sprocket. It will self clearance and show you what it's suppose to look like.
I was thinking the same thing! Actually counting on it lol
Progress!!
Yes sir!!
If you're going to do that on your big sprocket you need to get a vacuum chamber so you can suck out all the bubbles before you pour it
Nope that’s not needed with this polyurethane
Sprocket and track looked really good. How do you plan to tension the track?
Main tensioning comes from the wheel motor mounts having jack bolts. And also finer tuning with air pressure of the front tire.
@@CenterLineDesigns Thanks, very impressive build
Thank you
I’m running two ply 220 PIW belt on my DIY cat. Just built tracks in September. The belts have stretched ever so slightly which has also changed my pitch ever so slightly and caused me to build new sprockets. Not a huge deal, but something to consider. I think you’re running three ply? Can’t remember.
Okay good to know. Yup 3 ply 330. It will be interesting to see if it stretches
I wonder in your design of the sprocket, did you ever consider using a double sprocket with a spacer in the middle.
Yes I did at one point. I had god through many designs until I settled on what I am doing now. I was planning on doing a segmented sprocket that bolt onto a core. But I settled on a one piece design as I think it will work the best. Cheers
You will find that a metal sprocket will work better , plasma cut 1/2 inch thick metal and put a spacer in the middle to make it hit at the edge of the rubber track .
So a metal sprocket causes issues. Main one is that it will wear the track out. I designed a specific wear point that is the sprocket. I think folks will be surprised at how well it will work
It probably would be better if you were to change the 2 teeth into a single tooth and shape them to engage smoothly also giving them more strength for the torque they are going to receive under load
No that’s actually a very big waste. It’s an odd number tooth so every rotation the grouser changes groves. Ie ever grove sees a grouser ever second rotation. It’ll wear half as fast
I have seen where people use heat gun to get the air bubbles out
Yes I totally forgot about that trick. I’ll definitely try it when pouring the full size ones
If your sprocket ID doesn’t work, try routing out a piece of UHMW.
I previously thought about that route but after taking with plastics manufacturers they said UHMW is not good for that. Nylon is but it’s very expensive. Polyurethane is what you want. That’s why it’s what companies use
Since you have delete every other grouser why not do the same on the sprocket. It will make the sprocket teeth stronger and you can design the approach and departure angle of the teeth to suit the engagement of the grousers.
odd count of teeth on the sprocket, doubled wear life
So it’s an odd numbered sprocket. That means that a grove only sees a grouser every second rotation. This makes most efficient use of the polyurethane and will only wear half as fast!
did you have your belting pre stretched?
I am not aware of belting needing to be pre stretched. I bought it from a company that sells a lot of belting for rock crushers and they said this is what they sell for snowcat tracks… so.. I guess we will find out
Make a metal sprocket but coat the teeth with the epoxy
I thought about that but I wanted to avoid the adhesion issues to metal. I felt more confident that this will work with less issues
Is that a Spacely sprocket or a Cogswell cog?
Pardon?
@CenterLineDesigns it's a reference from an old cartoon " The Jetsons "
Oh hahaha. I used to watch the Jetsons but that definitely went over my head
i didn't see any "draft" built into your mold. You might be better to put 2 degrees of draft into your mold or use a silicon mold. Best regards Sarah
Draft?
@@CenterLineDesigns Molds are usually designed with the sides angled outwards between 2 and 7 degrees this is called draft and is used to enable clean release from the mold. If you have to have no draft the usual solution is to use a multipart mold.
Absolutely but that just doesn’t work for my sprocket design. Hence why I said it is just a sacrificial mold.
@@CenterLineDesigns Fine I look forward to seeing your snocat finished it looks an awsome project
Making some mold adjustments. Your comment resonated with me