DP420 Not working?

[mvly]

Ok I have given up on the DP420 method of securing Doc's Torque arm.

Here is my previous thread on me questioning on the DP420:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=42986&hilit=+DP420

This is the 3rd time it failed and this time much worst, though I have to admit, I am using regen quite a bit lately. Both sides failed at once during a downhill regen of 1.4KW back into the battery. The last time I epoxy, I left it for a week to cure and sanded the surfaces to ensure a clean contact. I guess that didn't help at all.

Now here are the possible solution.

1) I can file down the torque arm so it has a groove to slip around the aluminum dropout. Then i would use DP420 to secure it. The DP420 seems to work well in sticking, but not so well when you actually apply torque on it. I guess the sheer force is much less. The only downside is, there is only 1/2 the width of steel holding the axle. This might not matter, as it is harden steel. But it might eventually cut into the axle causing the axle to fail.

2) Drill holes into the dropout and the torque arm and use a steel screw and nut. Then DP420 everything together. This method might weaken the dropout.

3) build another 2x thick torque arm such it will fit like in 1), but have the same thickness as before. This method might be expensive as I will need to have someone cut and build me a new torque arm similar to Doc's but with a groove like in 1).

4) Weld Doc's torque arm to the aluminum dropout? I don't know if this will work as it's different material (harden steel and aluminum). It might overall weaken the dropout if the weld is not perform correctly.

5) Don't run regen anymore. I really want to avoid this because regen saves my brake pads and disc rotors. Also it's just cool to say to everyone my bike has regen. : )

What is your thoughts guys?

 

[amberwolf]

I'd go with #2; it's already been done and seems to work. I forget who did that but I think it's in the thread about doc's plates in the forsale section.

 

[Philistine]

I had the exact same problem as you. At first they worked but then after a few rides the epoxy failed. In the end I just drilled through the torque arm and frame and used high tensile bolts with nylock nuts to secure it on, and it has worked a treat. The torque arm is surpisingly easy to drill through if you use a quality bit. I did it in stages with a thin bit then widened the hole with the bit that matched the bolt. Cheers, Phil.

 

[bigmoose]

Doc's our epoxy expert, but you may have clamped it on so tight while the epoxy was wet that you squeezed all the epoxy out of the joint. There has to be a certain film thickness in the joint, I am not sure how thick, but your photo looks like the joint ended up "dry."

 

[dogman dan]

Screwed glued and tattooed is the expression. Or belt and suspenders. The point is, use two methods to secure what you really need secured.

I'd go with the screws and the epoxy. Be very carefull mixing the epoxy. Maybe you got too much hardener in it? The too dry comment makes sense too.

Also, the surface of the torque plate is very smooth. Maybe rough it up good with hacksaw kerfs? Shallow dill holes?

 

[ohzee]

Yea that sucks and 3 times around especially.

I know when I installed my plates I used my dremel to really scruff up the bike where
they went and also the torq plates as well. I use regen and push up to 6-7k at times with
no issues.

I agree on drilling holes , at this point you need something's that's going to give more faith
in them holding. GL

 

[Doctorbass]

mvly, i see you did not got the best results and i'll try to help you with that.

At wich temperature did you cured it and how much time?

I think that your situation might not be the best.

I explain:
-the surface area that your stock dropout have is minimal so you have less surface of bond and the torque arm surface is not all used.
-when grinding the torque arm, the grinder disk should be brand new or should not have any old grease in it from previous usage on contamined metal... otherwise this will contamine the part you try to grind.
-the best curing is at 100 degree for an hour and then you let it stabilize for 1 hour.. i explained taht in the previous pages of that thread... epoxy is not crazyglue.. it dont bond in 5 minute... the chemical process must have time to stabilize!

Could you take a closer picture of the torque arm and your dropout.. i wannan see how it broken apart.

Doc

 

[bigmoose]

Doc how about the epoxy film thickness? How thick should it be between the dropout and your torque arm?

 

[mvly]

At wich temperature did you cured it and how much time?

The first time, I left it for 2 days @ ambient room temperature
The second time, I left it for 1 day @ ambient room temperature
The Third time, I left it for 6 days @ ambient room temperature

I don't have an oven I can use and I cannot remove the rear swing from my bike that easily.

Could you take a closer picture of the torque arm and your dropout.. i wannan see how it broken apart.

I don't have any other picture. If you look at the other thread I posted, you can see the cracks. It starts to crack and it rotates. I think regen is too strong, but it's the lowest level I can set using the Lyen Controller programmer.

I'll bring it to a PE I know who specializes in build structural stuff. I hope he has a recommendation/solution.

Worst case, I will try the DP420 again. But this time, I will probably have a thicker layer between the two metal and probably scrap the both metal to have grooves so the DP420 can really get into those crevice.

 

[ohzee]

You cant take a carboard box and a hair dryer to make an oven ?

That's what is meant by that.. I even used my heat gun.. Mine was far from perfect it was just
enough to trap the air and keep the heat up.

 

[John in CR]

DP420 doesn't need heat to cure unless you're in a hurry. It cures to full strength in 24hr at room temp. See 3M's tech sheet http://solutions.3m.com.au/3MConten...5&assetType=MMM_Image&blobAttribute=ImageFile

Build your own clamping type torque arms which was always the correct solution. Making a welding shop friend is a great asset for any DIY ebiker without metal working capacity, and every one of them that I've met love the whole concept. It's something new and interesting for them. Their scrap bucket or box will have perfect material, and by showing interest in helping make them is a big plus because they love teaching someone interested, so bring a pair of safety glasses, which are cheap and also work great for night riding eye protection.

John

 

[Doctorbass]

You cant take a carboard box and a hair dryer to make an oven ?

That's what is meant by that.. I even used my heat gun.. Mine was far from perfect it was just
enough to trap the air and keep the heat up.

Yes.. this is what i suggested in this thread... this is the best oven you can make for big parts.. it can reach easy 70 celsius and accelerate the curing really fast and it is better

Doc

 

[bigmoose]

So I went looking for the answer to optimum bond line thickness for epoxy, because I didn't know the answer. Turned out it was thinner than I expected at 0.005 inches or 0.13 mm.

Here is the article: http://www.masterbond.com/techtips/understanding-bond-line-thickness

For relatively flat bonding surfaces, a bond line thickness of 0.005 inches results in achieving optimal shear and tensile strength properties.

 

[MadRhino]

Glue can be very tough, on my dropouts it never had a crack and they've been beaten quite bad this season. Nevertheless, so many factors can affect the strength of glue... What if the glue had suffered freezing before you bought it? How old is it? How good was the mix, prep job and curing process? That is why I have solid bolts in the first place, if the glue fails I can rely on them and it makes the whole job much safer. Glue has the advantage of making a barrier between alu and steel, saving a lot of contact corrosion.

 

[Punx0r]

I haven't seen anyone mentioned degreasing the parts?

Carb cleaner, acetone, cellulose thinners, panel wipe. As as with painting metal. Also, don't then go a put oily fingerprints on straight after