Fin alignment: jig, sight, or ?

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Viperfixr said:
Would really like to see this for HPR application, like on a 38mm min diameter build I am about to start. Any pictures? $$$?
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I made a 3 fin set for Modemmisuser for a PR 3" kit with g-10 fins. I can make just about any tube/fin thickness/ number of fins you would like. Here is a cad drawing showing the layout. They cost @ $20 a set plus shipping. They are infinitly reusable as epoxy won't stick. I will try to upload photos of a 4 fin set tonight.

View attachment SKMBT_C25309102710490.pdf
 
A few days ago, I was putting on some fins and I stumbled on what turned out to be a really good way to get fins on straight. I use the same type of foamboard template that others have mentioned, but I combine that with a piece of angle iron on the body tube. The angle iron sits very squarely on the tube. I just rotate it onto the fin and it locks the fin in place. The pics illustrate the process. Obviously, this only works if the main surface of the fin is flat, and the angle iron size would need to be reduced for smaller tubes. This is very easy and foolproof.

Jim

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A couple of times I have thought about buying one of the Rose or HPR-1 fin jigs, but the owner never answers emails. Likely, it is a bad sign for customer service.
 
cwbullet said:
A couple of times I have thought about buying one of the Rose or HPR-1 fin jigs, but the owner never answers emails. Likely, it is a bad sign for customer service.
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I've always found High Tech Rocketry incredibly responsive to emails, both before and after the sale. Absolutely great company to do business with!

If you want to put fins on straight there are lots of ways to do it. But if you want world-class-competition-straight, there is only one commercial tool available and there's a reason it costs so much. I've never heard anyone say they didn't think they got their money's worth out of a Rose fin jig.
 
I have emailed high power rocketry at least 6 times in 3 months and not one response. I understand that he took the HPR-1 off the market, but I asked about the rose fin jig also. He does not respond.
 
JimJarvis50 said:
A few days ago, I was putting on some fins and I stumbled on what turned out to be a really good way to get fins on straight. I use the same type of foamboard template that others have mentioned, but I combine that with a piece of angle iron on the body tube. The angle iron sits very squarely on the tube. I just rotate it onto the fin and it locks the fin in place. The pics illustrate the process. Obviously, this only works if the main surface of the fin is flat, and the angle iron size would need to be reduced for smaller tubes. This is very easy and foolproof.

Jim
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Great tip, Jim!

Greg
 
I rubber band two wooden L shaped pieces of trim wood to the body tube, attach a fin and then position the Ls so thet are snug against the fins. This really works well for me for all LPR and MPR.
 
I actually have always wanted a HPR-1 fin jig by Art Ross. I have tried many others. I will keep try to email them.
 
GregGleason said:
Great tip, Jim!

Greg
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Thanks Greg. That post was over a year ago. Now, I use two pieces of angle iron - one on either side of the fin. This literally locks the fin in position parallel to the body tube, and the template keeps the fin perpendicular to the tube. Sounds like the same setup Marlin mentioned with the L-shaped trim I would guess. I don't think a fin jig would do any better.

Jim

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Nice idea. The problem with these is it is still dependent on getting the fins perfectly at 120 degrees,
 
cwbullet said:
Nice idea. The problem with these is it is still dependent on getting the fins perfectly at 120 degrees,
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If you're referring to my post, what I do is produce the template in powerpoint (I can match the tube diameter and then have lines for the fins that are exactly 120 degrees). I also add multiple parallel lines for each of the fins so that I can choose which set of lines to use based on the thickness of the fins.

Then, I tape the guide to the foam board and cut out the pattern with an X-acto. I would say that getting the 120 and perpendicular to be exact takes just a bit of technique - a first-timer might make two patterns and get two foam boards. But with the angle iron, the process of getting the fins on exactly straight is easy and foolproof (with one piece of angle iron, it's almost foolproof, with two pieces, it is foolproof).

A couple details. Angle iron isn't always straight. Check the ones you get by setting them side-by-side and verifying no gaps (which would indicate that the pieces are not parallel to each other). The size of the angle iron can be varied to fit the rocket. Also, you might note in my picture that I have cut out holes for the angle iron around each fin opening. I think that cutting out one set, and then rotating the template, is probably better form.

Jim
 
JimJarvis50 said:
Thanks Greg. That post was over a year ago. Now, I use two pieces of angle iron - one on either side of the fin. This literally locks the fin in position parallel to the body tube, and the template keeps the fin perpendicular to the tube. Sounds like the same setup Marlin mentioned with the L-shaped trim I would guess. I don't think a fin jig would do any better.

Jim
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Great idea, Jim. Seems like this is one of the cheapest ways to get on fins on straight with some degree of precision.

That prompts another question that I can't figure out: What is the process that you use to apply adhesives from the fin to airframe? There doesn't look like there is much room to manuever, so it looks like it might be a stepped process.

Greg
 
GregGleason said:
Great idea, Jim. Seems like this is one of the cheapest ways to get on fins on straight with some degree of precision.

That prompts another question that I can't figure out: What is the process that you use to apply adhesives from the fin to airframe? There doesn't look like there is much room to manuever, so it looks like it might be a stepped process.

Greg
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Yes, cheap is an advantage too, but you know that's not why I use it.

On this method, the initial attachment is just along the root. I use CA if I'm in a hurry and slow epoxy if I'm not. I have also done this using slow epoxy along most of the root, but 5-minute epoxy at three spots along the root (i.e., front, middle and back). That approach lets me move along more quickly without sacrificing much strength.

Jim
 
I have the BMI jig, in addition to the Art Rose, and don't like the BMI jig at all. It might be OK for larger rockets, but the uprights just flex too much in the grooves of the base in order to maintain their accuracy for smaller rockets. It's just a poor design to allow for a slip fit of the uprights into the grooves. There's no good way to have enough clearance for a slip fit, yet at the same time have enough rigidity in the uprights. He should have designed in some sort of holding feature like set screws.

I also had some significant problems with the owner of BMI initially refusing to replace some of the uprights that were way out of tolerance, until I threatened to sue him. He only manufacturers part of his product (can't remember which part), and it's tough for him to ensure a good fit between the uprights and grooved base when both parts are manufactured in different facilities. One of my centers posts also wouldn't not even fit into the hole in the base despite me putting one part in the oven and the other in freezer, per BMI's instructions. Eventually did get replacement parts but my uprights still wiggle in their slots.

For the price, it's also ridiculous that his product is not adjustable for differing fin thicknesses other than manually shimming them.
 
Last edited:
Often the terms "jig" and "fixture" are confused or used interchangeably; however, there are clear distinctions between these two tools. Although many people have their own definitions for a jig or fixture, there is one universal distinction between the two. Both jigs and fixtures hold, support, and locate the workpiece. A jig, however, guides the cutting tool. A fixture references the part.

in other words a jig guides a tool such as a sanding block or a drill bit.

A fixture fixes a part(or parts) in place ,, such as a fin fixture
some people will also refer to it as a workholder

Estes calls their fin fixture a fin alingnment guide or tool, and not a "jig".

I deal with these things alot at work and have been corrected (as the old craftsman I work with will often do.)

more detailed distinction can be found at the Carr Lane website (one of the leading manufactures of jigs and fixtures for as long as I can remember)
lots of confusion out there especially on the web, but there is distinction

jig guides tool
fixture holds part

probably wont change anything... just a fwiw
 
Stymye said:
Often the terms "jig" and "fixture" are confused or used interchangeably; however, there are clear distinctions between these two tools. Although many people have their own definitions for a jig or fixture, there is one universal distinction between the two. Both jigs and fixtures hold, support, and locate the workpiece. A jig, however, guides the cutting tool. A fixture references the part...
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Thanks for the clarification.

Greg
 
For me it's just been eye balling the fins and using the fin guide that ESTE'S has on the market. You know the one with the yellow tube marking disc and ruler? I'm in the market for something more advanced in accuracy.

There are a lot of great ideas on the threads for aligning fins and some great jigs...take your time and look around and try to find one that will accommodate your needs.

Apogee sells a couple nice ones...
 

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qquake2k said:
I made two homemade fin alignment jigs. The smaller one for up to BT-60 or 70, and the bigger one for BT-70 and up. They work great. I just started using bungee cord and a cord lock on them. Works better than the elastic.


]
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I think you have more tools,jigs,ect in your shop than this guy...


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The body tube I am using has slots cut already from the bottom up to the length I need. I was thinking that when I attach the fins to the MMT outside of the airframe, That I could use the body tube slots to make sure they are straight. Would this technique work?
 
kokodog said:
The body tube I am using has slots cut already from the bottom up to the length I need. I was thinking that when I attach the fins to the MMT outside of the airframe, That I could use the body tube slots to make sure they are straight. Would this technique work?
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With TTW fins I use the body tube to make sure they are straight relative to the length of the body tube (that is close enough for my work) however I still use something to make sure that they are plumb. I print a template from the payloadbay website and then transfer that to foam board.
 
I either use the Estes fin aligner IF the fins will work with or or eyeball the alignment if the fins have a steep sweep angle. So far by putting your eye dead-center of the nose cone you can get the fins pretty straight that way.
 
blackjack2564 said:
Jon, you haven't mentioned what size rockets.....for airframes 2in and up I use homemade jigs made from foamboard or heavy cardboard modeled after this jig.
https://www.vatsaas.org/rtv/construction/finjig.aspx


Simple and easy to make. For estes type rockets I still just eyeball them

It's more of of thrust thing for me. If I do make a smaller high power rocket, like a minimum diam 29mm 0r 38mm I will use a jig.
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When using this jig, do you tack down all the fins at the same time?
 

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