Trying some drill holder ideas

[daniel banquo merrick]

I don't seem to have any of the bayonet drill holders anymore unless I can't find them. I don't think I will make them again because they take too long to make and are perhaps more complex than I would like. The grips have never been perfected because it is a challenge to make a strong, durable grip that will also allow the springs to move.

So I have been working with high strength hex bolts because the steel is really tough, they are easy to find and they have a head which can be incorporated into the holder. I am using a standard 7/8" hex bolt.

I turn down the hex head until it is 1.250" diameter, smooth and round. I turn down the top of the head until what remains is 1/2" thick. I make a groove for a leash and I cut it off so the length overall is 3.5". I drill it out about 2 5/8" deep to fit the shank of an SDS drill bit. In case someone wants to fit a 1/2" bit, I also drill out the first inch to 1/2".

I drill and tap for two 1/4 - 20 hex screws. The set screws I buy have a nylon patch on the threads so they do not jiggle loose like the old Pika drill set screw did. The set screw requires a 1/8" Allen key. I don't know how long the nylon patch will last but they are cheap and plentiful from McMaster Carr so if they start to work themselves loose, I will simply replace them.

For the grip on first holder I bought a product called Versimold which is a silicon rubber that comes as a putty and can be easily formed. It is vulcanized by heating it to 250 degrees F turning it into a solid but fairly soft rubber. It sets up to Shore A 46-54 which is about the same as a soft white pencil eraser but much tougher. It smells funny but not bad.

The Versimold easily bonds to itself but doesn't stick to anything else so I drilled four rows of dimples in the shank of the bolt with a 3/8" drill bit so that the grip is mechanically locked in place. The grip should not rotate or slip off but testing will tell. In the photos the rubber portion of the grip is 3 inches long and 1.25 in diameter. I made a cap for the drill end that is the same diameter as the head so all I have to do is roll it on a flat surface to get a uniform thickness. I rolled it on some 1/4" plastic mesh to make a sort of knurled surface.

I also bought a supply of Allen keys with a plastic handle which makes it easy to attach a cord and hopefully makes it harder to lose.

[daniel banquo merrick]

I am working on the second idea which is a handle molded onto the shank using urethane. I made a model grip out of aluminum which is simply a tube that fits over the bolt shank. The aluminum model has grooves lathed and machined into its surface in hopes of making it grippy. I will use the aluminum model to cast a 2 part mold into which the machined bolt can be inserted and the urethane poured.

The urethane is a curing two part liquid. I've picked a harder material (Shore A70) which is very tough and has a high tear resistance. I will still make the dimples (perhaps grooves) in the bolt shank even though the urethane should bond to the steel. Even if not needed, the dimples will lighten the holder.

Urethane tends to be slippery so I am not sure this idea will work out.

[mungeclimber]

first thought is that leash groove will really allow the leash to spin nicely.

[susan]

Looking good. Looking forward to hearing how these work out.

[daniel banquo merrick]

I made a couple urethane holders. Cosmetically they probably aren't so great but I think they are functionally good. The Shore A 70 urethane rubber feels better that I thought it would. It feels grippy enough. I made circumferential and longitudinal slots in the steel so the grip should not rotate or slide off. The rubber seems tough and tear resistant. Specs:

Mix Ratio: 2A : 1B by weight
Mixed Viscosity (cps): 3,000 (ASTM D-2393)
Specific Gravity (g/cc): 1.04 (ASTM D-1475)
Specific Volume (cu. in. /lb.): 26.5
Pot Life: 30 minutes (73°F/23°C) (ASTM D-2471)
Cure time: 16 hrs (73°F/23°C)
Color: Light Amber
Shore A Hardness: 70 (ASTM D-2240)
Tensile Strength (psi): 750 (ASTM D-412)
100% Modulus (psi): 250 (ASTM D-412)
Elongation @ Break: 750% (ASTM D-412)
Die C Tear Strength (pli): 200 (ASTM D-624)
Shrinkage: < .001 in./in. (ASTM D-2566)

In the photo you can see the two holders I've made, the aluminum form for the mold and the mold which I made from the same urethane material. The first holder has some clay (used to seal the mold) embedded in it and the bit end of the steel is slightly off center. For the second one I used some clear silicone grease to seal the mold so it doesn't have junk embedded in it and I fixed the mold setup so it stayed centered. I think the first one is as functional as the second but doesn't look quite as nice.

I could buy pigment and make the grip anything from black to fluorescent pink. They have some bubbles inside. There are also the positive and negative impressions of bubbles on the surface which only make them grippier.

If anybody is doing any drilling and would like the first one for prototype testing, it's yours so long as you use it and let me know the good and bad.

[John]

Aren't we going to see you in a few weeks in hand drilling land? We can test it then, right? Looks wonderfully hand crafted, and has "personality". I vote for hot pink pigment.

[daniel banquo merrick]

If I go I may not be doing any drilling. Here's my elbow today. Maybe you can bring some syringes and fat needles - if you do, I'll let you drain it. "Popeye Elbow" AKA bursitis.

[John]

Wow, that is trippy. I hope it isn't from too much hand drilling!

[susan]

Yikes. I hope you are seeing a doctor for that and hope you heal fast. No more hammering for a while for sure.

[YETI]

Sweet handles dan!  Hope to get around to doing new stuff again, so I can give em a test ride.

I blew out my bursa sack on my right elbow drilling and nailing on a route.

Heinous injury, but then after laying off it just "got better"

Hoping you feel better.