Author Topic: Prop mold (Read 2884 times)

Joe M · « **on:** April 04, 2020, 09:35:13 PM »

Made a propeller mold over the past week. Used a Zinger 12 x 5 wood prop.

Joe

Joe M · « **Reply #1 on:** April 04, 2020, 09:38:28 PM »

Used Epoxy resin and carbon tow to make one. The first one stuck in the mold and a few chips out in the hub area. Waxed a few more times and the second one pulled out with no flaws.

Joe M · « **Reply #2 on:** April 04, 2020, 09:42:32 PM »

The wood prop weighs 22.7 gram and the carbon fiber is 37.1 The cool thing on the epoxy one it can be heated up and de pitched. It also is much stronger than the wood one.
Joe

Joe M · « **Reply #3 on:** April 05, 2020, 12:50:55 PM »

I use Resin services resin and surface coat. The molds are waxed and a brushed coat of PVA, When dry lay up.

I need to work on my lay up of tow as the prop tips take less tow than the hub area. It you dont have the lengths correct the mold takes to much force to close and compact the roving and could lead to a weak part.

Joe

Dennis Toth · « **Reply #4 on:** April 05, 2020, 03:01:48 PM »

Joe,
Looks good. Did you post cure the resin? Wayne Trivin was a good friend that developed a technique for molding props and tanks. He passed away in 2005 but his website has been maintained by the speed and racing group. Here is the link: http://www.nclra.org/TechTopics/WayneTrivin/Actualindex.html

If you are looking to just re-pitch the prop, wood props can be heat pitched just like Carbon. The way you heat the wood prop is important. The technique is to heat and soak like pitching an IC APC prop. I use a heat gun. I am a bit lazy and only pitch the 70% diameter. So what I do is heat the hub by rotating top to bottom for about 20 ish seconds then let it soak in for 20 seconds then repeat. At this point it could be a little warm (near 175F) so either use a glove or a towel, grab the hub and twist the blade and hold for 15 seconds. Now check the new pitch, repeat as needed to get the desired pitch.

Best, DennisT

Joe M · « **Reply #5 on:** April 05, 2020, 04:11:37 PM »

Well Thank you for the information on changing the pitch on wood props, I have never heard that and will sure try it. The reason for the mold of the Zinger is due to not many in existence in my area.

Motorman thank you for the information as you have experienced what I am after on the lengths of tow and on laying up props.

Joe

Dennis Toth · « **Reply #6 on:** April 06, 2020, 11:30:06 AM »

Joe,
I have heat re-pitched the wood props for about 4 yrs. I found out about it from a discussion on this forum when someone mentioned that the Yatsenko props could be heat pitched. To me wood is wood so I got out an old 10x6 TF, my pitch gauge and heat gun and tried it. Dam if it didn't work just took the heat soak to get it to move just like doing an APC. People said it will go back as soon as it gets in the sun and warms up. I put it on the dashboard of my car that sits at work in the sun for 8 hrs. Came home tested, no change. I found you can easily go 1 pitch up or down and with some additional soaking cycles as much as 2 1/2.

The resin you used where did you get it and what harder and ratio goes with it?

Best, DennisT

Joe M · « **Reply #7 on:** April 07, 2020, 09:30:31 AM »

Dennis the resin can be bought at Aircraft Spruce. I use HTR-386 hardener that cures overnight but gives a good half hour working time if not in a confined cup.

Some more testing, since im bored

Cut my tow pieces in length, the lay up had very little flashing when dry but had a void on the hub which means I need to bulk up that area a little more. More testing necessary for the proper lay up
Joe

Joe M · « **Reply #8 on:** April 07, 2020, 07:12:12 PM »

Very nice mold you have made motorman

I sand off the flashing with a flat block and 80 grit, It is around 10 to 15 thousand thick. I now wear leather gloves as the fiber is as sharp as a razor. Ask me how i know.

This prop is going to be sacrificed to the saw blade to see how well it is compacted.

Dennis Toth · « **Reply #9 on:** April 08, 2020, 07:14:43 AM »

Joe,
Does the resin you are using require a post "bake" cure? When I did this we used Shell EPON resin (see Wayne Trivin site), it is very stiff but needed to be post baked for final cure. I made a plywood box with 4 100W light bulbs to be the kinda "easy bake oven". Would bake for 4 - 6 hrs. I also used unidirectional carbon sheet and cut out different lengths to fill the mold (also did just the tow). The carbon sheet was just much faster then the individual tow strains.

How stiff did the props turn out?

Best, DennisT

Gerald Arana · « **Reply #10 on:** April 08, 2020, 11:35:52 AM »

Quote from: Motorman on April 05, 2020, 03:39:40 PM

When I start with a wooden prop with full hub, I reduce the hub thickness by half.......

Why don't you just buy an electric APC prop of the pitch/dia. you want and mold it instead of modifying a wood prop?

Just curious, Jerry

Mike Hazel · « **Reply #11 on:** April 09, 2020, 01:21:06 PM »

Being a prop maker (and seller) I always find these threads plenty interesting. Just some misc comments: As previously mentioned it is important when cutting your tow to have plenty of stagger in the lengths so as not to have heavy "steps" in the material along the prop span. Generally I will do one inch increments so that makes plenty of different lengths. I have well over fifty props in my listing, which is way too many to mentally keep track of. So I have a "recipe" sheet for every one of them. Regarding resin, the Shell resin is my favorite and while a post cure is not absolutely necessary I find it makes the product more consistent and ready for immediate use. Without a post cure the prop can take several days to achieve full strength. My post cure is to put them in the oven at 175 degrees on a pan and then just turn the oven off and remove when totally back to room temperature. Another resin I have used is "aeropoxy" from Spruce Aircraft. Works ok, but a little thicker viscosity than the Shell product. Regarding filling the hub area...... I mix up a blend of fine fiberglass powder and chopped carbon fiber tow and using the same resin make a thin paste to build up hub area with no voids.

Joe M · « **Reply #12 on:** April 09, 2020, 08:26:07 PM »

Mike thank you for your information. My last prop was made with the tow cut in 1 inch length differences. I was wondering on using ground glass and tow as a filler. I will see how my next one turns out.

Joe

Lauri Malila · « **Reply #13 on:** April 10, 2020, 03:07:01 AM »

You can also buy the chopped carbon. Mine is chopped to 220my. It's short enough to make a smooth paste but still long enough to add strenght to mix. L

John Leidle · « **Reply #14 on:** April 10, 2020, 02:21:44 PM »

Joe ,
Thanks for posting this . it is an excellent article.
John L.

Larry Renger · « **Reply #15 on:** April 17, 2020, 02:16:13 PM »

Has anyone tried adding micro balloons to get the weight back down? It seems to me that the carbon provides the strength and the epoxy is just there to stabilize it and provide shape.

Joe M · « **Reply #16 on:** May 13, 2020, 09:48:25 PM »

Well more experimenting.. Lets try a 3 blade now. Took 2 props, 12/4 and split them at the hubs in Thirds to where I could use the bore as pivot to align the blades. I got all blades in proper orientation and pitch and glued them together. I now have a perfect prop to mold when I get some time. It should be easy to pitch up or down with a little heat after a prop is made of epoxy and carbon.

Joe

Joe M · « **Reply #17 on:** May 13, 2020, 09:55:00 PM »

As I look at this picture I think I should blend in the blade at the hub area.
Joe

Joe M · « **Reply #18 on:** May 14, 2020, 08:31:22 AM »

Motorman some more draft angle would make the fiber propeller come out easier when dry. Being a low pitch prop the hub thickness is around .375 after I joined and sanded out. Could prolly take off another .030 off the hub on the back side of prop and still be safe. Ill have to look at when I get home later. Would also like to get rid of the square tips but may just do that on the fiber props after dry/ Will see.
joe

Joe M · « **Reply #19 on:** June 01, 2020, 05:24:48 PM »

My 3 blade prop mold turned out great and the 1st propeller is a success. I looks like the carbon laid prop is double the weight of the wood one. It will probably loose a couple grams when dry and i am able to sand out and balance. It is definitely a stout prop thou.
Joe

Joe M · « **Reply #20 on:** June 01, 2020, 05:28:58 PM »

Im thinking a modification to the mold will be making some u shaped bolts that will allow me to tighten up the mold halves after lay up carbon and epoxy to aide in clamping tightly. My C clamps only reach in so far on the mold.
Joe

Reptoid · « **Reply #21 on:** June 01, 2020, 11:39:13 PM »

Just a tip. If you're going to go to all the labor of love making propellers from your own molds; don't start with a Zinger wood. One of the poorest blade shapes, airfoils, and grossly fat leading/trailing edges on the planet.

Joe M · « **Reply #22 on:** June 02, 2020, 03:52:49 AM »

Hey motorman I will read up on your thread after work today, Thanks
Joe

Joe M · « **Reply #23 on:** June 02, 2020, 04:02:33 PM »

Your thread on prop mold making is very informative motorman. I like the way you made the form with the 3 wings for the blades. Looks like it is thick and will allow a good pressure from the clamps to compress every thing when you lay a prop up. You have influenced me. Haha
That is where my mold is lacking. I will build up some bulk on my mold and Tri-wing it.
I guess the Epon epoxy you used is poured into your forms?

Joe

Joe M · « **Reply #24 on:** June 03, 2020, 08:44:43 AM »

I have witnessed the to many strands in the lay up and had to pull some out to allow the molds halves to close with out force. I also torque the clamps to let the epoxy oosze out and re tighten them like head bolts. I cut up some tow in 1/8 to 3/16 length and use in the hub area to build up bulk and at the tips to hold the strands together

The first propeller didnt take to much sanding to balance so I must have layed up the tow pretty evenly around the 3 blades. I am using 48k tow. I hand sanded to keep the hazardous dust at bay.

Keeping notes and making a few changes for the next prop lay up. Fun stuff

Thanks for your information
Joe

Joe M · « **Reply #25 on:** June 08, 2020, 03:38:05 PM »

3 Strikes but not out

Joe M · « **Reply #26 on:** June 08, 2020, 03:43:27 PM »

Home run,
each one a little better but I now know how much epoxy and carbon tow to make one. I did as Motorman and trimmed my mold and now I can put on clamps and lock it down evenly..

Seems like a 12 inch prop are all at 50g, Just alot of area on the thick blades. These sure are stout thou compared to a wooden prop.

Joe

Next up carbon spinner, Just because i like to experiment

Joe M · « **Reply #27 on:** June 08, 2020, 08:37:07 PM »

Yes I started to grind out one to see how deep the void was but not worth it since I now have the proper amount documented to do it right the first time. A small void I would possibly fill. voids on all 3 of the blades, NOT
While laying up tow I added some cut carbon strands in the hub area on subsequent layers to build up the hub so no voids,

With the mold trimmed like that I can get 20 + spring clamps on it. even squeeze out and no voids.

Thanks for your help MM
Joe

Joe M · « **Reply #28 on:** June 09, 2020, 09:45:42 AM »

They are all in the garbage and picked up. Sorry

Mark wood · « **Reply #29 on:** October 05, 2020, 08:22:26 AM »

I'm curious about what casting resin you used to make your mold with. Seems most of it is mucho spensive...

Mark wood · « **Reply #30 on:** October 05, 2020, 01:53:05 PM »

Quote from: Motorman on October 05, 2020, 11:41:19 AM

Go to post 28 in this thread then follow the link to post 59 in my thread.

Motorman

Thanks MM

Reason I asked the OP is perhaps he is a CAB like me and had a less expensive solution than the 655/101 products. By the time I get enough resin here to do what I want to do, it will cost most of a Benjamin on top of nearly another Benjamin for EPON/3234. I found some casting resin on the bay for $40 shipped which will be sufficient for the testing I want to do. I may just use WS 106/206 for some initial molds since I have it on hand already.

CAB - Cheap Ass Bastard

Air Ministry . · « **Reply #31 on:** October 05, 2020, 10:15:55 PM »

" Could prolly take off another .030 off the hub on the back side of prop and still be safe. "

Need to watch getting the blades to far back, they start rubbing backplates & nosecones etc . So a bit of forward set is often usefull .

Are you checking widths and depths on blanks with a vernier ? . obviously need two matching props for three blade . If found they can vary between batches .

A High AR 4 blade'd be intresting , still , I'll take the lot . Como 51 & FSR 45 run on 4 in. pitch .

Are you doing em for a specific plane or engine ?

Good to see, thankyou .

Randy Powell · « **Reply #32 on:** October 07, 2020, 01:57:45 PM »

I get molding materials from Tap Plastics. They have a variety including prototyping material and longer use material. I've never done props (I suppose I could) but have done cowls, landing gears of all sorts, bellcranks and various parts without issue.

Mark wood · « **Reply #33 on:** October 12, 2020, 07:07:28 PM »

Quote from: Motorman on October 05, 2020, 08:29:59 PM

I have used regular Bondo from Walmart when I want a cheap fast mold. You can see some of them on my thread. You have to keep the cross sections even or it will warp. You have to work fast between mixing and pouring, it dries quick. They are not as sturdy and require careful handling. Gluing plywood backs on each half helps allot.

Motorman

I've made lots of props but always in aluminum epoxy molds. When I lived in Indianapolis the epoxy was easy to get. I live in Wichita now and I have no clue where I can find it and none of the folks I am around have one either. Now, if I want a CNC milled mold that is easy but pricey. Being the CAB I am, I ordered some not so spensive epoxy on ebay thinking it would be good but I'm still waiting.... I'm not always the brightest bulb in the box. I don't think bondo will get the results I need. I've got to have repeatability which the epoxy molds will get. Ultimately I'll invest in aluminum mold if necessary. Actually, I'll buy a Machining center and do what ever I want.