Quantcast

Rail Button: How easy should they slide?

The Rocketry Forum

Help Support The Rocketry Forum:

TheBru

Member
TRF Supporter
Joined
Sep 14, 2020
Messages
23
Reaction score
7
Location
Portland, Me
I'm working on my first MPR (LOC Graduator) and am using rail buttons for the first time. I have test fit everything together but find that when I slide the rocket on to the rail it seems to catch or bind a little on the way down and the same if I push up from the motor mount after the rocket has been fully loaded onto the rail (to simulate a launch with wildly less force). It is a new rail and new buttons so I don't think its a dirty type of thing but was curious if it is an expected behavior that sorts itself out when you use an actual motor.

I assume this is not a unique to me issue and was curious to hear what others think and how they ensure everything comes off the rail nice and smooth.

Thanks
 

heada

Well-Known Member
Joined
Jan 18, 2009
Messages
3,603
Reaction score
839
Location
Indianapolis, Indiana
With the rocket on the rail and the rail standing vertical, you should be able to lift the rocket with little to no friction on the rail buttons. It should slide up and down freely. When loading onto the rail, its not uncommon to get a few catches or hang-ups.
 

mikec

Well-Known Member
Joined
May 9, 2009
Messages
2,443
Reaction score
348
It's hard to know for sure but it sounds like your buttons may be slightly misaligned or out of plumb. With a pristine rail and buttons things should be pretty smooth.

It might not matter depending on how tight they are.

Pics might help.
 

dhbarr

Amateur Professional
Joined
Jan 30, 2016
Messages
6,713
Reaction score
1,219
Do you have three buttons or only two ? Which buttons, and which rail ?
 

TheBru

Member
TRF Supporter
Joined
Sep 14, 2020
Messages
23
Reaction score
7
Location
Portland, Me
It's hard to know for sure but it sounds like your buttons may be slightly misaligned or out of plumb. With a pristine rail and buttons things should be pretty smooth.

It might not matter depending on how tight they are.

Pics might help.
Thats a great call out. Both buttons are on the same line but the forward button is just slightly angled.

Any advice on how to ensure the buttons are at a right angle to the body? I assume I need to remove one (or both) and re-install to get the fit just right.

(please ignore my poor fillet skills, learned a TON on this build so far)

rail buttons.jpg
 

heada

Well-Known Member
Joined
Jan 18, 2009
Messages
3,603
Reaction score
839
Location
Indianapolis, Indiana
Thats a great call out. Both buttons are on the same line but the forward button is just slightly angled.

Any advice on how to ensure the buttons are at a right angle to the body? I assume I need to remove one (or both) and re-install to get the fit just right.

(please ignore my poor fillet skills, learned a TON on this build so far)

View attachment 435637
yup, that'll add just enough friction to make it difficult to slide.

If you didn't attach them into centering rings, you might be able to tweak them to one side and get them to line up better. If you can't tweak them or they're into rings, then I'd remove them and move them to a new section and try again. Pick up a section of aluminum angle from the local hardware store. It'll help you align things like this.
 

Voyager1

Well-Known Member
TRF Supporter
Joined
Oct 23, 2015
Messages
555
Reaction score
181
Location
Oz
Are the buttons free to rotate, or have you tightened the screws down completely? If they can rotate, they might then have a small lateral movement that might correct your slight angular misalignment.
 

TheBru

Member
TRF Supporter
Joined
Sep 14, 2020
Messages
23
Reaction score
7
Location
Portland, Me
Are the buttons free to rotate, or have you tightened the screws down completely? If they can rotate, they might then have a small lateral movement that might correct your slight angular misalignment.
Interesting. So your saying to keep the button free to spin so that in case of a slight misalignment the button just acts then as a roller?
 

Voyager1

Well-Known Member
TRF Supporter
Joined
Oct 23, 2015
Messages
555
Reaction score
181
Location
Oz
Yes. If the button is free to rotate, then there is less friction along the rail. Some button attachments are designed to allow the button to rotate.

You need to make sure that the screw through the button is secure and won’t release from the body tube.
 

mikec

Well-Known Member
Joined
May 9, 2009
Messages
2,443
Reaction score
348
I don't leave my buttons free to rotate (that might help, or not), but I just barely stop them from rotating; they'll bind if they get too compressed.
 

crossfire

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 16, 2011
Messages
4,349
Reaction score
456
I don't leave my buttons free to rotate (that might help, or not), but I just barely stop them from rotating; they'll bind if they get too compressed.
I agree with you.
 

TheBru

Member
TRF Supporter
Joined
Sep 14, 2020
Messages
23
Reaction score
7
Location
Portland, Me
I don't leave my buttons free to rotate (that might help, or not), but I just barely stop them from rotating; they'll bind if they get too compressed.
this is a good point. I tried a couple different levels of tightness and there was a point where it wouldn’t slide but backing the tightness off proved helpful.
 

jrap330

Retired Engineer, NAR # 76940
TRF Supporter
Joined
Jan 25, 2020
Messages
439
Reaction score
129
Location
NJ
Thats a great call out. Both buttons are on the same line but the forward button is just slightly angled.

Any advice on how to ensure the buttons are at a right angle to the body? I assume I need to remove one (or both) and re-install to get the fit just right.

(please ignore my poor fillet skills, learned a TON on this build so far)

View attachment 435637
Fillets are fine...
 

TheBru

Member
TRF Supporter
Joined
Sep 14, 2020
Messages
23
Reaction score
7
Location
Portland, Me
Thanks everyone for the advice! I was able to get out and launch this past weekend. Two successful flights and one ~1k ft nose dive but it survived and will fly again!

Flight 1: E23T-5, 255AGL
Flight 2: F27R-4, 435AGL
Flight 3: G53FJ-7, 967AGL (assuming that a chute packing error prevented the chute from deploying correctly)

TBD:
Flight 4: G64W-7, ??? (using data from the first 3 flights to correct my sims and will fly again once I can!)
 
Last edited:
Top