Easy Research Rocketry Cutting and Coring Jigs - Tutorial

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patelldp

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I'd like to take a quick post to provide a tutorial on how to use the Easy Research Rocketry Cutting and Coring Jigs. They are currently in stock and available in both 29mm and 38mm sizes!

29mm Cutting and Coring Jig

38mm Cutting and Coring Jig


These jigs make cutting and coring propellant quick and accurate using a utility knife, drill bit (5/16" for 29mm, 1/2" for 38mm), and power drill. No lathe necessary!

Step 1: Cutting your propellant grain to length

1. Gather your Cutting and Coring Jig (body and spacer), necessary drill bit, hand drill, utility knife, and a stick of freshly cast propellant!



2. Remove spacer from the body. Insert the propellant stick into the body of the jig until it bottoms out. The propellant stick should be a nice snug fit that doesn't spin freely, so you may need to peel or friction fit to achieve the proper fit.



2a. Bonus pic: just to show what I meant above, I drew a line at the top of the jig to show how the cutting jig spacing works. That line is 2" from the end, perfect!



3. Use your utility knife to cut through the grain using the body of the jig as a guide. Apply even pressure and gradually work through the grain making sure to keep the knife as perpendicular to the grain as possible.



4. Here's what the grain looks like after it has been cut all the way through. The final step is to gently push the grain out of the jig using a dowel or the shank of your drill bit.



Here are the four example grains I cut for this tutorial. Identical lengths and clean cuts!



After the jump: Coring your grains using the jig!
 

patelldp

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Step 2: Coring your propellant grains

1. Locate the spacer that came with the jig and insert it in the body of the jig until it bottoms out. This spacer is 0.25" long and is used to keep the propellant grain from being inserted completely into the jig while drilling. It also provides some relief space for shavings created while drilling.



2. Insert one of your propellant grains that you cut to length in the first step. As stated above, the grain will now stick out 0.25".



3. This next step is important: grab the body / spacer / grain assembly from step two in your non-dominant hand. Hold the body of the jig with your palm and all fingers except your pinkie. The pinkie is then wrapped gently around the exposed length of grain and is used to keep the grain from spinning.



4. Insert your drill bit in the chuck of your hand drill and tighten. With the drill in your dominant hand, insert the drill bit through the hole in the opposite end of the jig until it comes into the contact with the propellant.



5. With your drill on the slowest setting, SLOWLY drill into the grain until you are approximately halfway through. Make sure that you regularly stop to clear the bit of shavings and do not allow the shavings to bog the bit down. When in doubt, stop and clear the jig. Remove the grain from the jig. Here's what the grain looks like drilled halfway through.



6. First make sure the bit and jig are clean of large shavings, then re-insert the grain by putting the un-drilled face in the jig. Using the same care as stated above, drill into the grain until you have completed the core. Remove the grain, clean the jig thoroughly of shavings, and properly dispose of the shavings. You now have a perfect grain without the use of a lathe!

 

patelldp

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I'll end this tutorial with a quick and important safety disclaimer:

Always use care when machining or working with propellant. When in doubt, go slowly and be deliberate with your actions. Properly dispose of all byproducts, and be especially careful with the dust created with drilling propellant. Clean all drill bits or other tools used with oil such as WD40 to prevent excessive oxidation and rusting.

Have fun and be safe!
 

ttabbal

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Nice write up! I use a cordless makita drill, that stands up on its own. Then drill over a stainless mixing bowl to catch the shavings and dust. Helps keep the mess contained.

I've been using acetone for cleanup. Any reason to prefer oils? I forgot to clean a utility knife blade once, the speed of corrosion was impressive, thankfully on a cheap blade.
 

patelldp

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Nice write up! I use a cordless makita drill, that stands up on its own. Then drill over a stainless mixing bowl to catch the shavings and dust. Helps keep the mess contained.

I've been using acetone for cleanup. Any reason to prefer oils? I forgot to clean a utility knife blade once, the speed of corrosion was impressive, thankfully on a cheap blade.
Thanks! I have always wiped my drill bits down with a paper towel that has been sprayed with a bit of WD. The moisture prevents the dust from being spread by the paper and also keeps the drill bit from rusting. I always dry the drill bit with a paper towel before I use it to drill grains again.

Cutting and drilling over something like this plastic tray will also contain your shavings.
 
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DavidMcCann

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I've got a set of these for 29 and 38. I made, cut and cored my first batch of propellant (and successfully tested two motors) last week. The cores were simple and perfect using this tool. No way to tell it'd been drilled from both ends, just one nice smooth hole from end to end.

Thanks again Dan.

 

djs

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I've been using this tool for a little bit now, and it works great. My only request is that Dan makes a 54mm one. Not sure if anyone else is interested, but I still cut/core my 54 grains manually.
 

patelldp

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I've been using this tool for a little bit now, and it works great. My only request is that Dan makes a 54mm one. Not sure if anyone else is interested, but I still cut/core my 54 grains manually.
Shoot me a message with your grain length and desired core and I'll print you one.
 

BDB

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This looks like a handy tool, but I may be missing something here. (I'm a noob to anything beyond small sugar motors.) Is there an advantage to cutting cores to a given length as opposed to simply making them in casting tubes that are already the desired length?
 
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patelldp

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This looks like a handy tool, but I may be missing something here. (I'm a noob to anything beyond small sugar motors.) Is there an advantage to cutting cores to a given length as opposed to simply making them in casting tubes that are already the desired length?
Making sticks of propellant is just easier than cutting a whole bunch of casting tubes to length. You can also tamp down propellant in a long casting tube easier than in a short tube. My experience has been that the top 1/4"-1/2" of propellant typically has more voids than the rest of the stick and casting grains to length would multiply those voids across all grains. With a stick, you can just cast it a little long and discard the void filled top.
 

FredA

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This looks like a handy tool, but I may be missing something here. (I'm a noob to anything beyond small sugar motors.) Is there an advantage to cutting cores to a given length as opposed to simply making them in casting tubes that are already the desired length?
As Dan said, making sticks is easier to pack and you only need one casting base.
Plus, you can make propellant without committing to the motor geometry.

One downside to this jig is that it is setup for a fixed grain length and fixed core diameter.
 
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patelldp

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One downside to this jig is that it is setup for a fixed grain length and fixed core diameter.
Well yea, inherent to the design. The lengths and cores are chosen based on standard geometries. The 38mm will work well with 1G through 6G, for example. Once the core is drilled, it's easy to go larger if you step drill size up by 1/16" increments and go slowly.

EDIT: I should also say that if you'd like a different combo of grain length and core diameter, let me know and I can draft it up.
 
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emckee

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Dan,

How about a cap to slip over the top/outside of the coring jig with a different diameter (smaller) hole to enable more variety? Also, you could print holes in the side of the coring jig (finger sized) to allow access to the grain if someone wants to use the jig on shorter cut grains. i.e. you could slide it out (or hold it in) from the side. Has the added benefit of keeping your fingers away from a spinning drill bit.

Just a couple ideas.

-e
 

cwbullet

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Dan,

I bought a couple. Thanks. Have you though about a jig to assist with cutting grains to length?

Chuck
 

patelldp

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Dan,

I bought a couple. Thanks. Have you though about a jig to assist with cutting grains to length?

Chuck
Chuck,

I saw that, the 38's are finishing on the printer now and they go out today/tomorrow! Check out my tutorial, this is a jig designed to cut grains to length and core them.

Thanks again!
 

cwbullet

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I used this jig again this weekend. Thanks, Dan for a great product.
 

prfesser

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FWIW...in the past I used a snap-blade knife to score and to cut grains. I've since found (as others have noted) that a carefully-sharpened kitchen slicing knife (chef's knife or carving knife) makes cutting grains a lot easier. Wash with soap and water after use, wipe with WD40. Never use that knife for food. Ever.

Best -- Terry
 
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