How to shim centering rings????

Just got a new kit today, suppose to be a TSR, mach +. Centering rings do not fit. MMT will be held in crooked. What have you guys done to shim everything square?
MMT 1.610 OD
CR 1.631 ID
.021 difference
this is inside of CR to outside of MMT

CR 2.116 OD
BT 2.155 ID
.039 difference
this is outside of CR to inside of BT

David Schwantz said:

Just got a new kit today, suppose to be a TSR, mach +. Centering rings do not fit. MMT will be held in crooked. What have you guys done to shim everything square?
MMT 1.610 OD
CR 1.631 ID
.021 difference
this is inside of CR to outside of MMT

CR 2.116 OD
BT 2.155 ID
.039 difference
this is outside of CR to inside of BT

Click to expand...

Not knowing the thickness of paper card stock, could you use some small cardstock shims at 90 degree intervals (or less) around the circumference? Then a fillet of epoxy to fill the gap between ring and tube?

Alternately, since this is high power you might want to consider fabricating new rings for a proper fit. Up to you really.

Sounds like sh*tty Qc. I would sand the CR to fit or ditch the kit. My CNC cut Wildman and MAC kits don’t have that problem. Specifically on the Mac kit the part tolerance is so tight that the av bay pressurized and pushed the nosecone off when dry fitting a min diameter.

That’s why I love min diameter. No damn CRs. Some of those CRs always take a little TLC and user sanding. If it’s majorly off I would dump the kit into the trash can. Hopefully someone more experienced helps you.

Complain to the manufacturer. It’s probably just a mistake. They should make it right.

I had thought of using 1/64th ply as shims around the MMT and CR. But was hoping someone might have a better idea.

This is my 7th kit from them and there is always something not right. It is getting old waiting for replacements. I hate to be this way.

+1 on complaining to mfr. Alternately, for the motor tube surface you might get away with a single wrap of light fiberglass in between the centering ring and tube. Additionally, in all my high-power builds I remove the glassine surface where the centering rings will adhere to provide more bite for the adhesive. Sure, it increases the gap between ring and tube (what you're trying to avoid/fix) but it does help create a stronger bond.

David Schwantz said:

This is my 7th kit from them and there is always something not right. It is getting old waiting for replacements. I hate to be this way.

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Don’t hate being that way (other than going back for more). Why do you keep ordering from them? After 2-3 times I would suggest switching to a different company.

Try a kit from MAC performance rocketry. Not the cheapest kits but part alignment was the best of any kit I’ve ordered so far. Seriously it’s glove like tight.

https://macperformancerocketry.com/

The Wildman kits I’ve had requires some light sanding on CR but CR always was aligned and centered. Usually a nub on OD needed knocking lose. Madcow kits are also high quality I’ve heard. The customer service of those kit makers is excellent.

https://wildmanrocketry.com/

I really like the kits, and they have always made it ok with me. Even bending over backwards to get me stuff 2nd day. I did not come here to bash. Was hoping for some good ideas. Anyway, as it ended up, the 1/64 ply was way to thick, so I found a roll of very thin plastic that I have kept, horded, for about 20 years now, I made some shims out of that, put them in place and CA'd the CR to the MMT. Will add aeropoxy in the AM to finish the joints. Will also be able to remove shims after CA dry so they do not ruin the epoxy joint.

Andrew, I have not built a Wildman kit yet, but have used his NC on builds. They are very nice, so I can only assume that his kits are also. I have built 2 Madcow kits, first one spun cart wheels until I lengthened it. 2nd one you can read about. What MAC kits have you built?

I agree that the manufacturer should make it right. But if you want to go ahead with the fix, I keep gummed paper tape (the brown stuff for package sealing, not reinforced), wet-and-stick, for making spiral-wound tubes. I have both 0.005" and 0.007" thick so two wraps of the thinner stuff on the MMT should make it almost perfect, likewise two of the thicker and one of the thinner on the inside of the BT. If you want to try it, send me a PM with your snailmail and I'll send you a bunch of strips.

You can do the same thing with glue and cardstock. I just calipered a piece of 65 lb cardstock, it's 0.008".

Best -- Terry

Is it TTW? That might help things if the fin tabs can lock it down in the correct position.

David Schwantz said:

What MAC kits have you built?

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Currently building a Hyper54 min diameter but so far the part fit exceeds Wildman kits I’ve touched. And Wildman wasn’t bad.

So far it dry fits without any sanding from MAC. I’m impressed.

Wow, thanks Terry. But I did use some super thin plastic last night and have just checked after the glue has dried, Should be good. And I know these are just "toy" rockets, but I still want them to be right.

Nice Andrew, love the fin can.

David Schwantz said:

Just got a new kit today, suppose to be a TSR, mach +. Centering rings do not fit. MMT will be held in crooked. What have you guys done to shim everything square?
MMT 1.610 OD
CR 1.631 ID
.021 difference
this is inside of CR to outside of MMT

CR 2.116 OD
BT 2.155 ID
.039 difference
this is outside of CR to inside of BT

Click to expand...

You might want to purchase common thicknesses of centering rings. I use SIG and use their "lite" (~50% lighter than same thickness birch) aircraft plys to fabricate a 3rd centering ring in all my HPR. That is unfortunate it is not correct out of the box BUT it takes me (not a carpenter) about 45 minutes to MAKE a centering ring using nothing other than a Japanese razor saw and a Dremel to cut, shape and fit 1/4" ply rings, no problem. I believe you would have no issues and the razor saws are about 20-50$ on amazon. Best xacto like saw I have ever seen-very sharp. Center your MMT circle on the BT circle, measure for even around and cut. lite ply is a little fragile at the edges with thinner stock but the saw will cut either type of aircraft wood. The 1/4" sheet was relatively inexpensive from sig and I have made spare fin sets no problem in no time. Again, I am not a carpenter and not really that great with shaping wood in the first place. I have made bays based on popular designs as well. There is no better substitute for bad parts than having the right stock. We all likely keep extra tubes, couplers, extra parachutes, Nomex sheets, motors and epoxies etc. Why not have spare aircraft ply too? Hope it is fixed-can be frustrating during a build to have an abnormality present itself

Thanks downhill, I do have a couple of those saws myself.

Been in same boat couple of times and did not want to wait for replacements.
Masking tape is your friend,
Wrap it around outside edge to built up enough to fit right.
Use new box cutter blade or single edge razor blade & cut off excess flush on each side of CR, viola done.

Andrew_ASC said:

View attachment 373353 View attachment 373352 View attachment 373351
So far it dry fits without any sanding from MAC. I’m impressed.

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Andrew
The MAC kits look to be great quality. What is the weight of the fin can? I keep thinking it ads extra weight to the back.
Thanks

Strips of paper can be used as shims as well.

crossfire said:

What is the weight of the fin can?

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393 grams.

I would make some new centering rings. I have made plywood centering rings using the band saw to cut the outside and scroll saw to cut the inside. It works but requires a lot of hand sanding to get a perfect fit.