Delay drilling old school: 1/32" per second

[Buckeye]

I just received a bunch of Aerotech HPR loads. The RMS Plus delays are (L) or (14A), which is a nice touch and similar to CTI. I will need to do some drilling, but I don't care to buy 38mm and 54mm drilling tools at $20 each. Ironically, last year I picked up the $10 Universal Delay Drilling Tool, only to find that it is not "universal" at all. It only works for DMS motors. WTH?

So, I was wondering if the "1/32 inch per second of delay removal done manually with a 3/16" drill bit" is still a valid method. I also have tables of delay element lengths and instructions for drilling that I printed over 10 years ago. The length difference between S, M, and L delays in the tables work out to be 0.024" to 0.031" per second of adjustment. These old drilling rules worked well for me over the years, so I am just checking that they are still valid for Aerotech's latest products. Thanks.

 

[pyrobob]

Yeah, I'm not sure why the Universal Delay Drilling Tool was designated Universal, since as you point out it only works with the DMS motors without modification. To my knowledge the 1/32" per second rule of thumb is still valid. Back in the 90's we used a tire tread depth gauge like this https://www.amazon.com/dp/B0002STSQM/?tag=skimlinks_replacement-20 to help us out.

 

[rstaff3]

I don't know why the old skool rules wouldn't still hold. I drilled one last year with a drill bit and one of those shoulder stop things that you can screw onto it.

 

[markkoelsch]

Should still be valid. Drill away.

 

[Buckeye]

Cool. Thanks for the info. Drill, baby, drill....

 

[cavecentral]

The AT universal tool works off of the 1/32 rule. Add the 1/16" washer provided to change the -4 sec to -2 sec.

As far as I know all AT is 1/32". I can't say for other manufacturers.

 

[CoyoteNumber2]

I was at a launch recently and had a guy tell me one couldn't shorten delays without the manufacturer's delay adjustment tool.

 

[Nytrunner]

And the 1/32 per second seems to apply to Pro38 delays as well (1/4" bit though). I did a bunch of online searching and decided I'd chance it instead of buying the friggin tool.

Measured with a caliper, made a stop-band with ductape, and then used an xacto to cone the hole. Got a perfect delay time for my L1 cert flight.

 

[T-Rex]

I bought the $20 tool. The 2 delays I drilled came out way short, so I'm back to using a drill bit. I use the tool only to center the drill bit.

 

[tfish]

I've used one of these for about 15 years.

Tony

 

[rstaff3]

I have the Loki (CTI retagged), old AT and new AT. Got 2 of the three free. Still use a DIY regularly too. Last time was for a G74 SU.

 

[cavecentral]

I bought the $20 tool. The 2 delays I drilled came out way short, so I'm back to using a drill bit. I use the tool only to center the drill bit.

I think some of them needed adjusted (use set screw / move drill bit). After that, it would be the same as the drill bit method.

 

[rstaff3]

I think some of them needed adjusted (use set screw / move drill bit). After that, it would be the same as the drill bit method.

I remember that too. Mine was OK.

 

[dhbarr]

I've used one of these for about 15 years.

I can -almost- read the text on that. Looks like exactly what I was wanting!

Edit: how did I do?

The PEACH Pitter
For Aerotech Delay Elements
PEACH: contraction meaning PEppy And CHeap

1.
- 8/32 screw x 4" or 5"
- 8/32 wingnut
- 8/32 nut
- red paint or equal
- black tape or 1/4" tube

2.
- install both nuts
- file flat cutting edges on screw
- clean threads

3.
- file nut and screw flush when nut is bottomed
- paint flat of nut that matches flat cutting edge when nut is bottomed, color red
- paint matching cutting edge on screw, color red
- install black tape or 1/4" nylon tube grip on shank, glue
- one revolution = 1/32"
- 1/32" = 1 second shorter delay

Bob Fortune (C) 98
[email protected]
use at your own risk
please distribute freely without alterations

 

[Handeman]

IIRC In the days before they sold delay drilling tools the original instructions from AT on how to drill a delay was to look up the length of the delays used for the short delay and long delay. Subtract the length of the short delay from the length of the long delay and subtract the time of the short delay from the long delay. That gave you the length of delay grain burn for that amount of time. You then divided that length by the time difference and that gave you the depth per second to drill the delays. You were supposed to do this for each type of propellant and delay grain because they had different types of delays for different motors and even the same delays burned at different rates in different motors.

I think the 1/32" per second came about because that would generally get you to within a second of what you wanted.

So the question is, did they standardize the burn rates of the delays across all motors and propellants so the delay drilling tools work right?

 

[Steve Shannon]

Here's the 2005 aerotech document about delay modification:
https://www.aerotech-rocketry.com/c...tions/RDK_Instructions/rms_delay_mod_inst.pdf

 

[oddmanrockets]

I've always used a drill bit to shorten delays even on single use motors I've also figured out how to shorten estes 24 mm motors ( even though its against the rules and you will cringe watching me do it ) the Deltie Thunder flies better on a D-12-1 than a 3 second delay

 

[woferry]

Yeah, I'm not sure why the Universal Delay Drilling Tool was designated Universal, since as you point out it only works with the DMS motors without modification.

I may be remembering wrong, but I believe when the RMS-EZ motors were being sold with the complete floating forward closures, they were drilled-out the same way as the DMS motors are (through the charge well). So I think the 'universal' name was probably because it would have worked with both DMS and -EZ loads, but then there were issues with early deployment of the EZ closures (My first and only EZ load was an I357T that went ~8s early and the early chute deployment tore the rocket in half) and they went back to the RDK-style delay elements. Though it sounds like more loads are effectively coming with the -L (14s) delay rather than the -M (10s)?

 

[Andy Limper]

I am going to assemble one of these gems tonight and throw in my range box.....Thanks...Andy

 

[GregGleason]

I just used a hobby knife, Mark 1 eyeball, and TLAR.

Its worked for me, but YMMV.

Greg

 

[rstaff3]

IIRC In the days before they sold delay drilling tools the original instructions from AT on how to drill a delay was to look up the length of the delays used for the short delay and long delay. Subtract the length of the short delay from the length of the long delay and subtract the time of the short delay from the long delay. That gave you the length of delay grain burn for that amount of time. You then divided that length by the time difference and that gave you the depth per second to drill the delays. You were supposed to do this for each type of propellant and delay grain because they had different types of delays for different motors and even the same delays burned at different rates in different motors.

I think the 1/32" per second came about because that would generally get you to within a second of what you wanted.

So the question is, did they standardize the burn rates of the delays across all motors and propellants so the delay drilling tools work right?

I think it is because the amount burned during the motor's thrust is dependent on the motor design (propellant and pressure and ...). And they have a fixed length of delay element to deal with. At one launch I tried out a bunch of Loki motors while he was dialing in the delay design.

I bet the 1/32 was chosed because it gets close on all of them and nobody is capable of drilling a delay more accurately.

 

[tbonerocketeer]

I may be remembering wrong, but I believe when the RMS-EZ motors were being sold with the complete floating forward closures, they were drilled-out the same way as the DMS motors are (through the charge well). So I think the 'universal' name was probably because it would have worked with both DMS and -EZ loads, but then there were issues with early deployment of the EZ closures (My first and only EZ load was an I357T that went ~8s early and the early chute deployment tore the rocket in half) and they went back to the RDK-style delay elements. Though it sounds like more loads are effectively coming with the -L (14s) delay rather than the -M (10s)?

This is what I remember. I think it was planned to use rms ez on all reloads at some point.

 

[Cabernut]

Ive been wondering about this myself. I have the DMS tool already and some new RMS loads for which I dont want to buy a whole new tool. It appears at first glance that the only difference is the circumference of the indent that centers the delay grain.

Is that correct? Is all thats needed to use a "universal" tool with RMS delays is an extra centering ring?

 

[pyrobob]

Ive been wondering about this myself. I have the DMS tool already and some new RMS loads for which I dont want to buy a whole new tool. It appears at first glance that the only difference is the circumference of the indent that centers the delay grain.

Is that correct? Is all thats needed to use a "universal" tool with RMS delays is an extra centering ring?

Without the two in front of me.... There's a "cavity" in both, or what I believe you're calling the 'indent'. The DMS tool has a shallow cavity while the RMS tool has a deeper cavity. And, the RMS cavity diameter is sized to accept the RMS delay grains while the DMS cavity, well, is sized for something much larger; at least all of the DMS motor's I've drilled out the DMS tool did not have a snug fit around the yellow forward closure. Something like that .

 

[Cabernut]

Seems like it could be 3D printed, with the right measurements. Spend $4 on a print vs. $24.

 

[jimzcatz]

I was at a launch recently and had a guy tell me one couldn't shorten delays without the manufacturer's delay adjustment tool.

Total BS. We were drilling in the early 90s way b4 drilling tools.

 

[cavecentral]

Total BS. We were drilling in the early 90s way b4 drilling tools.

I agree with Jim. Worst case, just drill it before the launch if you know what you are flying. I never an RSO or anyone ask about how a delay was drilled before. I had people ask how to use the adjustment tool, or corrected people using it wrong (not taking out the washer for -4 sec).

I think I might start asking if anyone has a left handed delay adjustment tool I can borrow :cyclops:.

 

[Buckeye]

I had people ask how to use the adjustment tool, or corrected people using it wrong (not taking out the washer for -4 sec).

OK, I'll say it. The CTI drilling tool is a much better design and easier to use than Aerotech's offerings.

 

[Nytrunner]

Honestly, how critical is the centering ring? How critical is it to have the drill bit EXactly on point?
If I hadn't already adjusted a couple delays with a bare drillbit (eyeballing the center), I'd be less inclined to speak up.

 

[CzTeacherMan]

Honestly, how critical is the centering ring? How critical is it to have the drill bit EXactly on point?
If I hadn't already adjusted a couple delays with a bare drillbit (eyeballing the center), I'd be less inclined to speak up.

I often eyeball drilling delays. With CTI, I just use the tool as designed. With AT, I just eyeball. That way I always buy the longest delay and adjust as needed. There's always a 20% leeway anyway, so I figure it's not too critical. Never had any trouble doing it that way either. An extra second one way or the other isn't going to shred my rockets that fly on those size motors anyway. Besides, even a perfectly measured delay won't be perfect unless the rocket flies exactly straight anyway.