Payloadbay.com finwrap tool: Am I doing this right?

[brockrwood]

I am trying to make a 4 fin “finwrap” printout for a genuine Estes BT-50 body tube.

I am printing at 100 percent (“actual size”) to a Brother laser printer.

The finwrap doesn’t quite wrap all the way around the tube. See pic.

Am I doing this right? Should it meet perfectly at the edges of the wrap?

Putting the same tube on the Estes fin marking tool shows two fins just a hair displaced from where they should be.

Which tool should I trust?

 

[tsmith1315]

Am I doing this right? Should it meet perfectly at the edges of the wrap?

I'd say yes and yes.

Increase the print size little by little until it meets. You can measure between the fin marks while flat to verify they're equal, and then verify the last measurement across the seam as halves added together.

You can also measure your actual tube diameter and multiply by pi/4 to get what that distance should be for your tube.

 

[brockrwood]

You can also measure your actual tube diameter and multiply by pi/4 to get what that distance should be for your tube.

Need to find my digital micrometer, which I misplaced, darn it. It must be around here somewhere.

 

[brockrwood]

I'd say yes and yes.

Increase the print size little by little until it meets. You can measure between the fin marks while flat to verify they're equal, and then verify the last measurement across the seam as halves added together.

You can also measure your actual tube diameter and multiply by pi/4 to get what that distance should be for your tube.

There we go! A finwrap for body tube diameter 0.985 inches is exactly the same as the Estes fin marking tool.

Which, of course, begs the question of why I don’t just use the Estes tool?

The answer is I sometimes want to create a fin marking guide for a non-Estes body tube size.

Now I know what to do. Just keep adjusting the tube diameter in the payloadbay.com tool until I get the little printed lines to perfectly match up when the printout is wrapped around the tube.

 

[Sandy H.]

I'd say yes and yes.

Increase the print size little by little until it meets. You can measure between the fin marks while flat to verify they're equal, and then verify the last measurement across the seam as halves added together.

You can also measure your actual tube diameter and multiply by pi/4 to get what that distance should be for your tube.

Just double checking (as I screw myself this way sometimes too) but circumference is pi*d. I am usually calculating areas for work, so I'm always doing the d^2*pi/4, but I'm not sure if that's what you were getting at or if it is the fact that he has 4 fins and you were giving him the spacing between fins.

Its been forever since I've used the payloadbay version, but I know it is a good tool. I often find that people who write tools like that, though, don't account for paper thickness. It might be worth adding +0.006"/+0.008" to the 0.976" tube OD to get the rough OD of the finished wrap. Not sure if that is the source of error or if the printer is being a little bit tedious, which also happens.

Does the payloadbay tool include a 1" square on the template like some other template makers do? If so, print it at 100%, measure the square with calipers and adjust by the difference to get it spot on.

Also, to the OP: Good job on your diligence. If you used the template as-is, the rocket would fly fine I'm sure, but why not shoot for perfection if it is reasonable to attain with reasonable effort! [edit: OP posted the update before I hit save. I was referencing the original template with the small gap as being OK, but he made the change and got perfect. Which is . . . perfect!!!]

Sandy.

 

[brockrwood]

Does the payloadbay tool include a 1" square on the template like some other template makers do? If so, print it at 100%, measure the square with calipers and adjust by the difference to get it spot on.

It does include a “calibration” line at the bottom of the page! I wondered what that was for! Thanks!

 

[tsmith1315]

or if it is the fact that he has 4 fins and you were giving him the spacing between fins.

Yep, fin spacing.

 

[brockrwood]

The calibration line meaures EXACTLY one inch on my printout when I set the body tube diameter to 0.985 inches.

 

[Sandy H.]

The calibration line meaures EXACTLY one inch on my printout when I set the body tube diameter to 0.985 inches.

In theory, the 1" line will measure 1" no matter what the diameter. If you're changing the scaling in the print box, that would change the 1" line.

Either way, sounds like 0.985" is the solution for this tube. If you found your calipers, did the tube measure 0.976" or closer to 0.985"? I often put a motor or similar in when I measure thin tubes, as it is easy to make the calipers say whatever you want them to. The other method I use it to just creep up on the diameter while spinning the tube back and fourth. If you get a feel of friction, too far, start over.

Just my method, not at all the only way.

Sandy.

 

[brockrwood]

It’s the body tube. It is closer to 0.985 inches in diameter than it is to 0.976.

I just measured the circumference (laid flat) of the payloadbay.com finwrap printout set to 0.985 inches in diameter for the tube.

The circumference comes out to 3.094468764 inches.

That is 78.5995066056 mm.

The printout measures exactly 78.5995066… mm to my eye.

So payloadbay.com and the printer are very close to tge exact measurments I inputted into payloadbay.com.

That means the body tube, itself, is slightly larger in outside diameter than the specification of 0.976 inches.

How much out of spec?

0.985 - 0.976 = .009 inches bigger than spec. That is 9 thousandths of an inch bigger than spec or 0.9137 percent bigger than spec.

Hmm. Man, that fin position looked like it was off by more than 1 percent. I guess human visual acuity, at least for radial position of small objects, is pretty good.

 

[brockrwood]

In theory, the 1" line will measure 1" no matter what the diameter. If you're changing the scaling in the print box, that would change the 1" line.

Either way, sounds like 0.985" is the solution for this tube. If you found your calipers, did the tube measure 0.976" or closer to 0.985"? I often put a motor or similar in when I measure thin tubes, as it is easy to make the calipers say whatever you want them to. The other method I use it to just creep up on the diameter while spinning the tube back and fourth. If you get a feel of friction, too far, start over.

Just my method, not at all the only way.

Sandy.

Beat me to it! See my recent post.

 

[neil_w]

The thickness of the paper usually means that the circumference of the *fin wrap* is slightly larger than the circumference of the *body tube*. Therefore it is normal to need to adjust it slightly larger. Once you have found that adding .009" to the body tube size works well for your printer paper, that same offset should work for any body tube size.

I think TVM has recommended that you add about half the thickness of the sheet of paper to the body diameter for fin wraps, and .009" is pretty close to that as far as I know (for standard printer paper).

 

[brockrwood]

The thickness of the paper usually means that the circumference of the *fin wrap* is slightly larger than the circumference of the *body tube*. Therefore it is normal to need to adjust it slightly larger. Once you have found that adding .009" to the body tube size works well for your printer paper, that same offset should work for any body tube size.

I think TVM has recommended that you add about half the thickness of the sheet of paper to the body diameter for fin wraps, and .009" is pretty close to that as far as I know (for standard printer paper).

So 20 pound copy paper has a thickness of .009 inch?

I am just kind of surprised that my eyeball could see that small of a difference.

 

[Sandy H.]

So 20 pound copy paper has a thickness of .009 inch?

I am just kind of surprised that my eyeball could see that small of a difference.

A random piece of paper in my reach was 0.003" to 0.004" which is why I initially suggested 0.006"-0.008" as an adder. Apparently 0.009" worked better and matches TVM's experience.

The 0.976" circumference is 3.066", while the 0.985" circumference is 3.094", so 0.028" which is pretty close to 1/32" - pretty easy to see an error that big. That 3.14 multiplier helps a lot!

Sandy.

 

[brockrwood]

A random piece of paper in my reach was 0.003" to 0.004" which is why I initially suggested 0.006"-0.008" as an adder. Apparently 0.009" worked better and matches TVM's experience.

The 0.976" circumference is 3.066", while the 0.985" circumference is 3.094", so 0.028" which is pretty close to 1/32" - pretty easy to see an error that big. That 3.14 multiplier helps a lot!

Sandy.

So when Estes prints a “body tube wrap” for fin and launch lug placement in kit instructions, they must know in advance what thickness paper they will print the instructions on and adjust accordingly. Diligent work on their part.

 

[brockrwood]

A random piece of paper in my reach was 0.003" to 0.004" which is why I initially suggested 0.006"-0.008" as an adder. Apparently 0.009" worked better and matches TVM's experience.

The 0.976" circumference is 3.066", while the 0.985" circumference is 3.094", so 0.028" which is pretty close to 1/32" - pretty easy to see an error that big. That 3.14 multiplier helps a lot!

Sandy.

In the future, I will assume that the paper of the fin wrap itself adds about .008 inch to the tube diameter (because it adds thickness on both sides 2 x .004 = .008). I will start with the listed spec diameter of the tube and then add about .008 inch. Then I will print the wrap and test fit. Then I just keep adjusting the tube diameter in the payloadbay.com finwrap tool until the paper finwrap comes out just right, with both of the little marks meeting up perfectly.

 

[neil_w]

So when Estes prints a “body tube wrap” for fin and launch lug placement in kit instructions, they must know in advance what thickness paper they will print the instructions on and adjust accordingly. Diligent work on their part.

They don't always fit perfectly... if you read @hcmbanjo 's blog you'll find many instances of where the included fin wrap doesn't fit right and he has to go print his own.

 

[bjphoenix]

I just make my own. I wrap a piece of paper around the tube and with a sharp pencil I put a mark where the paper overlaps. I spread out the paper and using a metric ruler I measure from end of paper to this mark in mm. Then I divide this measurement by number of fins, start at the edge of the paper and put marks on the paper using these measurements. I do this in mm because I can estimate fractions of mm. For instance a BT-60 will measure about 131mm. Divide by 3 and this is 43.7mm. So I put marks at 43.7mm and 87.4mm. This will give proper spacing for 3 fins.

 

[brockrwood]

They don't always fit perfectly... if you read @hcmbanjo 's blog you'll find many instances of where the included fin wrap doesn't fit right and he has to go print his own.

The payloadbay.com tool works fine for me. All I have to do is adjust just a tiny bit two or three times and I hit the perfect size.

Payloadbay.com has awesome tools!

Who is this Roger Smith fellow who runs payloadbay.com? I need to thank him for the awesome tools at his website!

Is he a user on TRF?

 

[neil_w]

The payloadbay.com tool works fine for me. All I have to do is adjust just a tiny bit two or three times and I hit the perfect size.

Payloadbay.com has awesome tools!

Who is this Roger Smith fellow who runs payloadbay.com? I need to thank him for the awesome tools at his website!

Is he a user on TRF?

He is @jadebox on TRF. He is also the proprietor of jonrocket.com and runs rocketreviews.com.

 

[brockrwood]

He is @jadebox on TRF. He is also the proprietor of jonrocket.com and runs rocketreviews.com.

Mr. @jadebox! YOU ROCK! Thank you so much for giving the rocket-loving community payloadbay.com!