Building a Guillotine Fin Jig

I getting ready to build a Guillotine Fin Jig and noticed it calls for cabinet grade plywood. I was just wondering if anybody had constructed one from solid hardwood and if so have the jig alignments held true over time?

Grenadyr73 said:

I getting ready to build a Guillotine Fin Jig and noticed it calls for cabinet grade plywood. I was just wondering if anybody had constructed one from solid hardwood and if so have the jig alignments held true over time?

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Plywood is dimensionally stable since its plies alternate in direction. Hardwoods will expand and contract with changing climate. You'll lose your accuracy. Kitchen cabinets deal with this expansion and contraction by having the hardwood panels float in the frame. They are not glued in. I'd recommend just buying good multi-ply aircraft grade plywood for good long-term accuracy.

Trident said:

Plywood is dimensionally stable since its plies alternate in direction. Hardwoods will expand and contract with changing climate. You'll lose your accuracy. Kitchen cabinets deal with this expansion and contraction by having the hardwood panels float in the frame. They are not glued in. I'd recommend just buying good multi-ply aircraft grade plywood for good long-term accuracy.

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If you have a local wood supplier, the best product is baltic birch plywood, cabinet grade is fine and its cheaper than the aircraft grade plywood (no noticeable difference on a fin jig).

My Macklin Fin Jig works great - you'll definitely want whatever wood you use to be dimenesionally stable to keep things square and accurate.

I'll definitely be building my first one out of hardwood plywood but I may have to make one out of solid maple for the sake of comparison. I had a template laser cut for use with my router and am anxious to try it out. Thanks for the input.

You could use MDF instead of plywood. Still stable and might save a few bucks.

Baltic Birch is readily available from Hobby Lobby, Michaels and online vendors such Rockler, Woodcraft and Woodworkers Source. While a Guillotine made from solid hardwood such as Maple or Walnut would be beautiful to look at, warping, checking and splitting might well be a problem over time, especially where there are wide temperature and humidity swings. MDF would be a good alternative because it is dimensionally stable in a controlled indoor environment. However, it also devours tool bits and does not hold nails or screws.

Good luck with your build and let us know how long it takes. And pictures...or it didn't happen. :wink:

BTW, here's a nice rendition of my design by Australian Sascha Grant (AKA "Krusty" here on TRF).

https://www.flickr.com/photos/oflittleinterest/8243130563

Alright, plywood it is. A curly maple jig with stainless hardware and polished aluminum rails would have been a sight to behold though... *sigh* I don't think I could stand the shame of making it from MDF if anyone ever caught sight of it. Though, that laser cut one by Krusty was impressive.

I had a 1/4" thick mdf/melanine template laser cut for use with a router guide bushing and 1/4" spiral up bit to make my jig. I'm currently waiting on a bit and to pull the trigger on the wood before I begin. Fwiw, I also downscaled your (tmacklin) plans to micromaxx scale and laid them out for laser cutting. I may have to rethink the plans to make them interlock like Krusty's.

Also, thanks for making your plans available for purchase, that seems to be a rare thing and I appreciate it. The guys on The Rocketry Show podcast talk up your jig regularly and are the ones who turned me on to the jig and the plans.

tmacklin said:

BTW, here's a nice rendition of my design by Australian Sascha Grant (AKA "Krusty" here on TRF).

https://www.flickr.com/photos/oflittleinterest/8243130563

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Hi thanks to this post I checked out your website, and have a stupid question- the plans are for the small version...is it just a question of scale to get a larger version, or are the two substantially different?

soopirV said:

Hi thanks to this post I checked out your website, and have a stupid question- the plans are for the small version...is it just a question of scale to get a larger version, or are the two substantially different?

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Yes, the plans are for my original sized (or small) version which was based to accommodate all standard Estes sized tubing available in 2011, BT5 through BT80. My original units were made with a simple base of plywood, ripped to a set dimension which was 5 3/4" which also fixed both the fixed and sliding end panels at that same 5 3/4" width and thus one table saw set up. This dimension allowed for a square hole having a diagonal dimension of 3 3/4" and 1" of "meat" on either side for the vertical slots. This design was soon replaced by a boxed unit by the addition of side panels which were glued and nailed to the base and fixed end panels, adding rigidity to the assembled device as well as forming a guide pocket for the sliding end panels. This change also eliminated the aluminum guides which were a PIA to fabricate and install. (The plan set I sell shows an example device in which the original sizes have been rounded up to even dimensions, 4" rather than 3 3/4" and 6" rather than 5 3/4" and so on.)

Eventually , I contracted with Nat Kinsey (Upscale CNC) who now fabricates my end panels for all sizes made by me...small, medium and large. I recently crafted a mini-jig for Micro-max enthusiasts which is a very limited market. I still make the sides, bottoms and aluminum rails for everything that I sell, but the sides are now made of thicker plywood to allow for dadoes and slots receiving the end panels and bottom. The small unit has been slightly increased in size and now allows for full three inch thin wall paper tubing. All kits made and/or sold by me or Apogee come as a knocked down kit to be assembled by the purchaser.

The size of the device is not dependent upon any specific range of dimensions as it is governed only by the geometry, and an individual could make it anything he or she desires within the limits of the sheet goods one wishes to use. It could be wood, plywood, MDF, plastic, aluminum...whatever works. I can tell you from experience that it is easier to build a larger unit rather than a smaller unit. I hope this answers your question/s and thank you for your interest.

I recently got access to a laser cutter, so I'm going to try making one with 1/4" MDF

Ok, now lets back the bus up here. You can still have the beauty of curly maple (or my favorite of Coca bolo. Just apply a laminate facing to your wood. The catch is that you do have to face both sides to maintain stability.

1tree said:

Ok, now lets back the bus up here. You can still have the beauty of curly maple (or my favorite of Coca bolo. Just apply a laminate facing to your wood. The catch is that you do have to face both sides to maintain stability.

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Let us see some pictures of your progress.

Slightly off topic and more of a suggestion: having a small light like an LED right under the angle rails would help enormously in ensuring proper alignment. I actually caved and bought the jig, but discovered that it's still possible to misalign things because it's difficult to align the mark you make on the body tube with the V-shaped alignment notch because that area is in shadow. I tried shining a flashlight through the angle rails from the top but it's still difficult since I've only got 2 hands.

That brings up another recommendation: the shiny surface on the inside of the rails created mirror images of the V-notch, further confusing things. I'd recommend painting the inside surface flat black (or perhaps use a permanent marker) to prevent that from happening.

One final suggestion: It's not easy to perfectly align both ends of those L-angle rails. If it's off even a hair, it won't be perfectly parallel with your body tube. Result: fins not aligned longitudinally with your body tube (okay only if you want to induce a spin. I don't think that's the preferred intent in most cases). My fix was to simply print up a ruler scale on a narrow (1/8" wide) strip of paper and use clear mailing/box tape to attach it to the top of the vertically sliding box ends that the alignment rails rest on. "0" is dead center over the V where the body tube rests and the tick marks in 1/16" increments run in both directions 3" inches.

There may be more elegant solutions but these worked for me, and with a minimum amount of effort.

I think its an awesome jig and a great design.... my eyes aren't what like they use to be. I might get one later. This is a "want" not necessarily a "need" at this point.

I use scrap balsa of the same thickness as the fin I'm mounting declined at 45° to ensure the aluminum rails are parallel and centered.

I leave the right rail solid all the way through the build as well as the back left thumbnut, and only loosen the front left nut a halfturn or so when rotating to add a fin.

HTH,
-dh.

dhbarr I use the same method to space the rails the right distance apart to fit the balsa. The difficulty (for me anyway) is getting both rails absolutely parallel to the box and equidistant from the V-notch that the BT is clamped in. At both ends. Because the balsa thickness changes depending on the build (and I sometimes use more than one thickness in a build) I have to realign the rails often, and eyeballing it just wasn't accurate enough. I made the suggested fixes because the fins were still coming out tweaked after using the jig.

File a 45-deg bevel on the alignment scraps? But yeah, I'll be adding a ruler next time I break it out.

I can also speak for a small magnetic level to ensure the fin being jigged is purely vertical.

dhbarr said:

File a 45-deg bevel on the alignment scraps? But yeah, I'll be adding a ruler next time I break it out.

I can also speak for a small magnetic level to ensure the fin being jigged is purely vertical.

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dhbarr Great idea about the level. I have a small bubble level and never thought to use it for that purpose. I also have a small laser pointer that I could probably have used to make sure those rails are aligned longitudinally as well.

Just thought I'd attach a few pics to more clearly show what I meant. 1st shot shows the scale with tic marks that I attached to the end guillotine sliders. 2nd pic is a closeup with the aluminum rails in place. 3rd shot shows how the rails can be perfectly aligned longitudinally (to align with the body tube) by using the tic marks. dhbarr


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Yup, mine's getting that mod next time I have it out. Very nice!

Rktman said:

Just thought I'd attach a few pics to more clearly show what I meant. 1st shot shows the scale with tic marks that I attached to the end guillotine sliders. 2nd pic is a closeup with the aluminum rails in place. 3rd shot shows how the rails can be perfectly aligned longitudinally (to align with the body tube) by using the tic marks. dhbarr


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Nice mod, fyi there is a adhesive backed measuring tape that can be purchased that measures down to 1/32" increments.

rharshberger said:

Nice mod, fyi there is a adhesive backed measuring tape that can be purchased that measures down to 1/32" increments.

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rharshberger

Darn, which I'd known that. Would've saved me quite a bit of time (as long as I can get one 1/4" in height, which is the thickness of the ply that's available to stick this measuring tape to). I'll definitely keep it in mind if/when my home made laminated paper strip wears out, thanks!

Rktman said:

rharshberger

Darn, which I'd known that. Would've saved me quite a bit of time (as long as I can get one 1/4" in height, which is the thickness of the ply that's available to stick this measuring tape to). I'll definitely keep it in mind if/when my home made laminated paper strip wears out, thanks!

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They are usually about 3/8" to 1/2" tall, but maybe they could be cut down, usually they are either coated thin aluminum or aluminized plastic so they trim easily with a xacto knife.

Thanks, good to know!

Those are great when doing a lot of smaller rockets so you don't have to make a bunch of templates. For 3"-4" and up I use a template made out of 1/4" foamboard.
I was using plywood for templates and the foamboard is a lot less work.
First a jig to seat the 1st fin then 2nd one adjacent to it (on a 4 fin)
Once I set the 2 at 90 deg for the 4 fin, I use a plywood yoke to align the opposite pairs until done.
For the 3 fin, I just set the 1st then use the foambard for the other 2.



That method allowed this 9" Patriot to only rotate 200 deg through a 4000' flight. Good alignment is nice, wind shears and other forces can make any of them spin.


This kept me from making a huge Guillotine Fin Jig for the big stuff. I think that jig is ingenious.