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McMaster seal amount of squish

az_gila

Well Known Member
I started a new thread to get a specific answer. :)

I'm getting ready to make lots of dust and making the seal area of the doors ready.

Based on lots of other postings I bought most common the McMaster-Carr 1120-A411 seal - 1/4 inch web and a 3/8 bulb.

All of the posting seem to say to leave a 0.25 inch gap for the seal to squish into, but my initial checking of a foot or two seem to make the bulb too compressed.

This is about 0.25 shown in a C-clamp -

o7V.jpg


This is the view with an extra 1/16 inch gap -

o7g.jpg


Am I missing something here? It seems like the 5/16 gap would create a very adequate seal.

Did previous builders really use a precise 0.25 gap? Or was it "fudged" a bit larger?

My test areas have been in the middle of the sides and seem pretty representative.

Since the web needs sanding in spots and building up in others the seal I bought should be OK - I'm just not sure of the exact gap to make.
 
I?ve posted on this in the past, but perhaps you did not see it.

Before you dive into grinding away fiberglass, consider the much simpler option to put the seal on the door. Self adhesive seals from McMaster come in various sizes.

This has worked well for me - and is a good now as it was six years ago when I put them on.

Carl
79543-B07-B16-A-4-F69-934-A-C14-BA5-EC750-D.jpg
 
I?ve posted on this in the past, but perhaps you did not see it.

Before you dive into grinding away fiberglass, consider the much simpler option to put the seal on the door. Self adhesive seals from McMaster come in various sizes.

This has worked well for me - and is a good now as it was six years ago when I put them on.

Carl
79543-B07-B16-A-4-F69-934-A-C14-BA5-EC750-D.jpg

I agree with Carl here. Although I put my McMaster seal on the opening, I like the idea of it being on the door itself instead. It also eliminates the possibility of damaging the seal getting in and out of the cabin.
 
No results here yet. I did a minimum .025 gap with .025 material thickness. I
wasn't concerned if it got a bit bigger clearance in spots. My thought was that I could take it to 5/16 in spots if I have problems, as the mounting side of the seal can be squeezed down and still grab.

I stopped on the top to let my interior paint dry and moved to the panel. However, I plan to do the final install of the top next week and do final tweaking of the doors. At that point I will test the seals and let you know if it all worked.

Frankly, I think that I like the first picture with the tighter squeeze. It will likely seal better. The second pic looks like it is just barely meeting or coming up short on the recommended minimum of 1/2D compression.

Larry
 
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I?ve posted on this in the past, but perhaps you did not see it.

Before you dive into grinding away fiberglass, consider the much simpler option to put the seal on the door. Self adhesive seals from McMaster come in various sizes.

This has worked well for me - and is a good now as it was six years ago when I put them on.

Carl

I just prefer the idea of a solid locking tab to hold the seal in place - especially in a hot AZ hangar or ramp.

Interested in the gap dimension used for the 1120-A411 seal.

That's why I started a new thread...:)
 
No results here yet. I did a minimum .025 gap with .025 material thickness. I
wasn't concerned if it got a bit bigger clearance in spots. My thought was that I could take it to 5/16 in spots if I have problems, as the mounting side of the seal can be squeezed down and still grab.

I stopped on the top to let my interior paint dry and moved to the panel. However, I plan to do the final install of the top next week and do final tweaking of the doors. At that point I will test the seals and let you know if it all worked.

Frankly, I think that I like the first picture with the tighter squeeze. It will likely seal better. The second pic looks like it is just barely meeting or coming up short on the recommended 1/2D compression.

Larry

I tried a 2 ft seal test strip on the lower front side of one of the doors and it was almost impossible to push the door into place. I'll keep plying around making more dust...:)
 
I tried a 2 ft seal test strip on the lower front side of one of the doors and it was almost impossible to push the door into place. I'll keep plying around making more dust...:)

have you measured out the seal requirement to see how much extra you will have? I have been hesitant to cut a sizable piece off yet, reading that you will use most of the 25'.
 
have you measured out the seal requirement to see how much extra you will have? I have been hesitant to cut a sizable piece off yet, reading that you will use most of the 25'.

I just went and bought 50 ft, and I'll use the extra to make the 1/4 web wider where needed using it as a mold partly filled with flox. :)
 
Yes, but surely this will seal... :)

o7g.jpg

I would expect so. However, the manufacturer recommends a minimum or optimum amount of compression for a reason (can't recall the exact percentage), so I wouldn't simply trust the fact that it "looks like it will seal."

Larry
 
I would expect so. However, the manufacturer recommends a minimum or optimum amount of compression for a reason (can't recall the exact percentage), so I wouldn't simply trust the fact that it "looks like it will seal."

Larry

Good point on data....

First one I found was a Grainger identical part -

Although many mistakenly believe that a higher compression rate results in a stronger hold, our bulbs are designed and engineered to work best at 25-40% compression of its original height, with 25% being optimum. If you compress it more than that, its life and serviceability will be limited. When building your part, be sure to choose the bulb size that correlates to a 25% compression rate for your application.

https://vimeo.com/28068686

https://www.trimlok.com/rubber-extrusion/trim-seal/hatch

I can't seem to find a manufacture's detailed data sheet for the actual McMaster product.
 
Good point on data....

First one I found was a Grainger identical part -

Although many mistakenly believe that a higher compression rate results in a stronger hold, our bulbs are designed and engineered to work best at 25-40% compression of its original height, with 25% being optimum. If you compress it more than that, its life and serviceability will be limited. When building your part, be sure to choose the bulb size that correlates to a 25% compression rate for your application.

https://vimeo.com/28068686

https://www.trimlok.com/rubber-extrusion/trim-seal/hatch

I can't seem to find a manufacture's detailed data sheet for the actual McMaster product.

Well I am unhappily a part of the "Mistakenly believe" crowd. I would guess our seals are pretty similar if using the same type if foam EPDM. However, the Grainger seals look more oval than round, which may impact the desired compression level, as the round seals need more compression to become oval.

Larry
 
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Well I am unhappily a part of the "Mistakenly believe" crowd. I would guess our seals are pretty similar if using the same type if foam EPDM. However, the Grainger seals look more oval than round, which may impact the desired compression level, as the round seals need more compression to become oval.

Larry

The catalog pics show the bulb as being quite round, but I would like to see an actual spec. sheet or application note for the McMaster product.

https://www.trimlok.com/secure/content/documents/trimlok_catalog_72dpi+10132016.pdf
 
FWIW, Gil, and as detailed in another thread, I was shocked to find the 1/4" gap I had created was not enough to allow the door to close with the 3/8" bulb seal. Pin engagement was not happening no matter how I pushed. I took the gap wider, to .30" and still was not able to close the door.

Rather than grind further, which no doubt would have eventually allowed the door to close, I replaced the 3/8" bulb seal with a 9/32" bulb - 3/16" channel width seal. Perfect. I only have to add thickness to the door edges in a few spots because the narrower channel grips well to the thinner doorway edges that are left after all that grinding I did.

I don't know yet how well it will seal at the compression that's occurring, but I guess if I hear wind noise I can go back to the 3/8" seal or, perhaps more easily, add thickness to the door inner surface to increase the bulb compression of the smaller seal I went with. At this point I'm just delighted my doors finally close with a seal in place - and that without undue torque on the handle.
 
rear hinge gap

I don't know about the rest of you but living here in VT cabin heat can be an issue during winter. So I have spend at little bit of time looking for leaks. The biggest flow outflow of air for me is around the door seal near the rear door hinge. Because of the cut out required due to the hydraulic piston and hinge I am not getting a good seal with my Mcmastercard seal. I tried putting a piece of fiberglass across this area but interference with the piston resulted in me grinding/sanding a way a path for the piston and the recent cold spell has demonstrated yes I am still getting pretty good flow.

But I like the idea of putting the gasket on the door in that area. I am going to give it a try.

Thanks for the idea.
 
I ended up with around a 25% compression. The seal works fine with only that amount. I have been flying for 6 years and 900 hours and the seals still look new. You will never get the doors to close if you try to over compress the seal, I tried.....

img


40603910410_a30958e500_c.jpg
 
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I ended up with around a 25% compression. The seal works fine with only that amount. I have been flying for 6 years and 900 hours and the seals still look new. You will never get the doors to close if you try to over compress the seal, I tried.....
....

Bill, did that work out to about a 5/16 inch gap?
 
Bill, did that work out to about a 5/16 inch gap?

The base below the bulb is about .075", so 25% compression of the 3/8 bulb should net a .360" gap.

The 9/32" bulb would net about .280." Given that I followed other advise and set my gap at 1/4" maybe I will swap the 3/8 bulb for the 9/32 variety.

I am a bit concerned that my bulb came out of the package compressed a bit from round. if that is the norm, then we need a bit more compression to account for that.

Larry
 
The base below the bulb is about .075", so 25% compression of the 3/8 bulb should net a .360" gap.

The 9/32" bulb would net about .280." Given that I followed other advise and set my gap at 1/4" maybe I will swap the 3/8 bulb for the 9/32 variety.

I am a bit concerned that my bulb came out of the package compressed a bit from round. if that is the norm, then we need a bit more compression to account for that.

Larry

Since I'm still sanding and making dust so I can use the just under 5/16 dimension. I have the very lumpy green cabin cover so keeping the 1/4 edge thickness is going to take quite a bit of work anyway.

With your numbers, a 40% compression of the 3/8 bulb gives a 0.300 gap, just under the 0.3125 (aka 5/16) guess I made.

I think I'll simply aim for a 0.300 gap with my existing seal.
 
Gil, I don't remember the exact gap. Try a small piece and shoot for 25% and see what that gives you. I remember making a gap tool, I just don't remember the number...
 
Since I'm still sanding and making dust so I can use the just under 5/16 dimension. I have the very lumpy green cabin cover so keeping the 1/4 edge thickness is going to take quite a bit of work anyway.

With your numbers, a 40% compression of the 3/8 bulb gives a 0.300 gap, just under the 0.3125 (aka 5/16) guess I made.

I think I'll simply aim for a 0.300 gap with my existing seal.

Looking further at the McMaster-Carr catalog, this seems the way to go.

If in operation the bulb is not compressed enough or loses 'squish', the next size up seal is identical except for a 7/16 bulb instead of 3/8. This would be an extremely easy change to make if needed.

https://www.mcmaster.com/1120a421

Always good to have a back-up plan...:)
 
Sidebar

Mel, I was curious about some seals so took a piece of al sheet and attached a the seal around the perimeter, used spacers and clamped to a second sheet. Then pressurized it with a pressure regulator to see how it worked. You would not need more than 1.5 psi. Solid elastomer design guideline is 20% compression target. Like o-rings etc. A 16 in^2 test area is plenty.

My greatest issue on my tipper was the force per foot at compression. It was too much for the initial preload to fully engage the latches. So, a better seal can be too much, as you found out.
 
Finally got my doors fully mounted on the attached cabin top, after taking a break to do wiring, and thought I would post my results. I maintained a minimum gap of 1/4" and it varied to 5/16" is some spots. The vast majority was 1/4". I put on the 3/8" bulb seal and it was impossible to fully close the door, but none of the seal was fully compressed. I used a couple of clamps to help compress the seal in the upper part of the door and the pins went in without too much difficulty. I let it sit for 24 hours for the seal to take a "set." Next day, I am able to open and close the door without much difficulty. Over time, I expect it to get even better.

I was pretty concerned after reading and analyzing all of this, having already set up a 1/4" gap, but it worked out ok. If I was doing it again, I would shoot for a 5/16" gap with the 3/8" seal. That would leave the seal in it's optimum compressed position.

Larry
 
I just finished my door seals and woof, I made a lot of dust. The 1/4" was no where close to being enough of a gap, as others have mentioned. Mine does vary in spots, but I found having a sacrificial seal for the whole frame was easiest. I also wound up slicing the little rubber flap from inside the channel off to provide more clearance. I'll try and get a few measurements of the actual gap and post them tomorrow.
 
I just finished my door seals and woof, I made a lot of dust. The 1/4" was no where close to being enough of a gap, as others have mentioned. Mine does vary in spots, but I found having a sacrificial seal for the whole frame was easiest. I also wound up slicing the little rubber flap from inside the channel off to provide more clearance. I'll try and get a few measurements of the actual gap and post them tomorrow.

We must have different seal types. My seal has the rubber flap on the side of the channel opposite that of the bulb seal. Therefore it has no impact on the door to frame clearance. If the flap is on the bulb side of the channel on your seal, that may explain why you need more clearance.

Larry
 
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Larry, I have the McMaster Carr seal that fits 3/16" edge and has a 3/8" bulb. Interesting that your's has teh flap on the opposite side. Did you get your seal from Grainger?
 
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