AeroTech 75/2560 liner length

[Richardx]

I am trying to assemble AeroTech K1000T with RMS 75/2560 casing. Per instruction, bonded the grain and set it overnight. When I tried to assemble the casing next day, the threads wouldn't bite. The lining measure 11 1/2". Sizing chart I downloaded from this forum says it should be 11 1/16". Sleeve was 1/2" too long!
Contacted AeroTech and confirmed that the liner should be 11 1/16".
Here is the head scratcher. They are asking if I can shorten the liner?!?! How do you cut off near 1/2" of the sleeve with fully bonded K grains inside???
I am tempted to cover up the top of the grain and do a simple miter saw cut but worried about igniting the grain accidentally.

Any help would be much appreciated!!!

 

[manixFan]

A miter box with a fine-tooth hand miter saw. I have one with the adjustable pegs that lets you clamp the workpiece in place. I cut larger tubes all the time with it.

The other technique I use (although typically with smaller tubes) is a metal hose clamp large enough to go around the tube and then cut with a razor saw. I do that when I want a finer cut. I draw a circle all the way around the tube and use that to align the clamp edge. I always cut to the outside edge. When I am nearly done, I’ll loosen the clamp and rotate the screw portion out of the way, tighten it up and finish cutting. I’ve cut dozens and dozens of tubes that way, including fairly thin paper ones.

Neither method is very fast, but both can be very accurate.

Good luck!


Tony

 

[mhanna]

Oh boy, I have two K1000T's for a NASA SLI team going to Huntsville April 10th. I checked the tubes and they are very different. (I have not bonded the grains yet). One is 11 1/8th, probably not a problem - the other is 11 3/8th, which could be a problem when building the motor and tightening things down. So do I try and cut this down myself or contact Aerotech for replacement. If I'm modifying the motor does that make it an EX motor?

 

[3stoogesrocketry]

Oh boy, I have two K1000T's for a NASA SLI team going to Huntsville April 10th. I checked the tubes and they are very different. (I have not bonded the grains yet). One is 11 1/8th, probably not a problem - the other is 11 3/8th, which could be a problem when building the motor and tightening things down. So do I try and cut this down myself or contact Aerotech for replacement. If I'm modifying the motor does that make it an EX motor?

This would fall under "approved field modifications" . I built a K1275 last week that was a solid 3/16 to long. I noticed as I was dry fitting everything before assembly. I just used a good accurate chop saw to shorten the liner 1/8 inch.

 

[rfjustin]

Oh boy, I have two K1000T's for a NASA SLI team going to Huntsville April 10th. I checked the tubes and they are very different. (I have not bonded the grains yet). One is 11 1/8th, probably not a problem - the other is 11 3/8th, which could be a problem when building the motor and tightening things down. So do I try and cut this down myself or contact Aerotech for replacement. If I'm modifying the motor does that make it an EX motor?

Like @manixFan suggested above, miter box with a fine-tooth hand miter saw will get the job done with ease. Shorten the liner yourself, no worries, then bond them grains in.

 

[mhanna]

Not sure I have a "good accurate chop saw" to cut it with. Did you put the cut end at the top with the seal disk or at the bottom on the nozzle end?

 

[rfjustin]

Not sure I have a "good accurate chop saw" to cut it with. Did you put the cut end at the top with the seal disk or at the bottom on the nozzle end?

Cut is square are true does not matter which end you use. Miter box and hand saw is plenty good here, just take your time.

 

[3stoogesrocketry]

Not sure I have a "good accurate chop saw" to cut it with. Did you put the cut end at the top with the seal disk or at the bottom on the nozzle end?

Take a speed square and make sure your ay 90 degrees to the bed/blade. Or buy a cheap mitter box of Amazon, or this is the hardest one. Take your liner and slide it thru the case and use the case as a rest to carefully square up the liner when using a hacksaw to trim the liner. Yes I've done this in the field. Go slow

 

[jsdemar]

Always dry fit everything before gluing in the grains.

Liner length problems are happening often. They should publish a list of liner lengths for each motor to catch these issues.

If you don't feel comfortable cutting the liner, have @AeroTech send you a replacement.

Use the casing as a way to mark squarely around the circumference. Put some tape on the OD of the liner behind the cut to get a tight fit in the case. Use a sharpie marker around the liner using the case as a guide. Cut the liner with a fine saw blade slightly longer than the mark. Sand off the end until the line starts to disappear equally around the circumference. Sand the ID and OD edges.

I would use the factory cut end as the forward end with the seal disk.

 

[mtnmanak]

Always dry fit everything before gluing in the grains.
They should publish a list of liner lengths for each motor to catch these issues.

+1 - Could not agree more! Always check your liner lengths when you get the motor. Long liners are a pain, but easy to fix. Short liners will cause a CATO.

Just posted the dimensions I have here: https://www.rocketryforum.com/threads/motor-dimensions.185508/

 

[mhanna]

Thanks everyone, if this was just my rocket at our local field I would cut and go. Since this is a school that earned the right to go to Huntsville in a competition I contacted Aerotech. They will send me a new liner tube. Really glad I had not done any grain bonding yet.

 

[rfjustin]

Thanks everyone, if this was just my rocket at our local field I would cut and go. Since this is a school that earned the right to go to Huntsville in a competition I contacted Aerotech. They will send me a new liner tube. Really glad I had not done any grain bonding yet.

Hence my suggestion made in the grain bonding thread.
"Grain bonding weeks in advance allows opportunity to make sure you have all the parts expected in the reload, and if there is a hick-up there is time to address it..."
https://www.rocketryforum.com/threa...onding-to-the-liner-tube.185240/#post-2558677

 

[mhanna]

Yes sir!

 

[Richardx]

Thank you all! You all are awesome!
Karl from AeroTech recommended hand saw if the grains are bonded inside the sleeve.
Taking Tony's recommendation, picked up a worm gear clamp and fine tooth hacksaw. Went really slow and finished it off with some sanding and squaring. I am wondering if I should just glue the seal disk to the top of the sleeve.
Same model motor will be shipped directly to Huntsville for SLI competition. Guess I will be bring the hacksaw and clamp with me.

And yes! I will definitely check the sleeve length on all motors in the future.
To anyone using 75/2560, AeroTech stated

As for the liner length, they should be 11 1/16 plus no more than a 1/16 extra, we have been cutting all liners with the plus 1/16 to support the seal disc staying in place. Typically, you should see no more that a 1/8” gap at the nozzle end when the forward closure is seated.

Richard

 

[Richardx]

Not sure I have a "good accurate chop saw" to cut it with. Did you put the cut end at the top with the seal disk or at the bottom on the nozzle end?

When the grains were bonded, they naturally settled toward the nozzle end as the instruction says to cure it nozzle end down. So the extra length was all at the top where the seal disk sits.

 

[Richardx]

Always dry fit everything before gluing in the grains.

Liner length problems are happening often. They should publish a list of liner lengths for each motor to catch these issues.

If you don't feel comfortable cutting the liner, have @AeroTech send you a replacement.

Use the casing as a way to mark squarely around the circumference. Put some tape on the OD of the liner behind the cut to get a tight fit in the case. Use a sharpie marker around the liner using the case as a guide. Cut the liner with a fine saw blade slightly longer than the mark. Sand off the end until the line starts to disappear equally around the circumference. Sand the ID and OD edges.

I would use the factory cut end as the forward end with the seal disk.

If the grains weren't bonded, I wouldn't hesitate to use a chop saw to cut the extra length off and put that end toward the nozzle.
I thought about asking for a right length sleeve but I didn't want to mess with the bonded grain.

 

[rfjustin]

Thank you all! You all are awesome!
Karl from AeroTech recommended hand saw if the grains are bonded inside the sleeve.
Taking Tony's recommendation, picked up a worm gear clamp and fine tooth hacksaw. Went really slow and finished it off with some sanding and squaring. I am wondering if I should just glue the seal disk to the top of the sleeve.
Same model motor will be shipped directly to Huntsville for SLI competition. Guess I will be bring the hacksaw and clamp with me.

And yes! I will definitely check the sleeve length on all motors in the future.
To anyone using 75/2560, AeroTech stated


Richard

Nice work! You got that cut and cleaned up perfectly.