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Author Topic: DISCOVERY VALVE MOD: Angle drilling: HOW??  (Read 383 times))

Offline SILENT SQUIRREL

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DISCOVERY VALVE MOD: Angle drilling: HOW??
« on: February 20, 2021, 07:44:56 PM »
Hello to each of you
I thought I'd bookmarked a thread about drilling out a Discovery valve at an angle  to improve air flow.
Darned it if I can find it.
Can any one provide a link to info that shows how to do this, please?
(Or just tell me how)
Thanks
Ed
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Offline Gliderflyer

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Offline rsterne

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #2 on: February 21, 2021, 12:53:18 AM »
I use a milling attachment in my lathe.... The end mill is in the headstock chuck, and the valve is mounted in the milling vice and adjusted to an angle of 20 degrees to the vertical.... I mill it out with a 5/32" end mill....

Bob
  • Coalmont, BC, Canada
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Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline SILENT SQUIRREL

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #3 on: February 21, 2021, 09:48:30 AM »
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Offline SILENT SQUIRREL

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #4 on: February 21, 2021, 10:03:48 AM »
I use a milling attachment in my lathe.... The end mill is in the headstock chuck, and the valve is mounted in the milling vice and adjusted to an angle of 20 degrees to the vertical.... I mill it out with a 5/32" end mill....

Bob

Thanks, Bob
No lathe here.
But I do have a 12' bench top drill press with adjustable table (45* L&R)
Any ideas for a setup that is not destined to fail?
Thanks
E
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Offline nervoustrigger

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #5 on: February 21, 2021, 01:20:13 PM »
Note Bob is not describing a drilling operation but a milling operation, which is more akin to plunge routing.  Essentially a short and very stiff bit that cuts both on the tip and the side of the shank, not just the tip.

To do this job with a drill, a good approach is to fill the existing hole so there is material to support the bit as it plunges in.  For example, use threadlocker or bearing compound to set a stub cut from a piece of brass rod stock or something similar.  Or a piece of wood dowel secured with epoxy would be better than nothing, but the harder the species and the finer the grain, the better.  Otherwise it's likely to shred very quickly as you start the drilling and then you're kinda back where you started.
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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #6 on: February 21, 2021, 02:06:19 PM »
What I would do is secure it to your bench drill table at the angle wanted and go real slow and let the bit do all the work. Go slow enough that the bit is not deflected and you should be fine.

Iíve also used a dremel and carbide shaping bits to carve out my transfer port area and make it all flow smooth.
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Offline rsterne

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #7 on: February 21, 2021, 04:07:31 PM »
You can try making a crude 2-flute end mill from a 5/32" twist drill, if you can't obtain an end mill.... Shorten it until you only have a bit more drilling length than the depth of the hole you need to mill.... Grind the end off square, and then using a Dremel cutoff wheel create a bit of relief on the cutting end, so that it looks like a 2-flute mill... Chuck the modified drill up close in the chuck, set the valve up on the angle you want (I use 20 deg.), center the cutting end over the existing exhaust port, and proceed VERY slowly.... As long as the chuck spindle and the work vice are both rigid, you should get an acceptable result.... I would use at least 1000 RPM for that diameter in aluminum, and feed it VERY slowly.... Final finishing, eg. blending the port into the valve throat, can be done with a 1/8" spherical burr in the Dremel....

If you can get a 5/32" 4-flute end mill, you would be far better off, as the larger (more rigid) shank and proper cutting surface will work much better.... but I quite often modify a drill like this when I want a hole with a square bottom, and if kept short, they will cut somewhat like an end mill....

Bob
« Last Edit: February 21, 2021, 04:12:14 PM by rsterne »
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1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline SILENT SQUIRREL

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #8 on: February 22, 2021, 09:55:55 AM »
Thank you again, Bob
It seems to me the low cost of a 5/32" 4 Fl end mill outweighs the PITA of modifying a drill bit.
And will do a better job.
I can then put the tool making effort into making a stable jig
Take care & stay safe
Ed

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Offline rsterne

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #9 on: February 23, 2021, 01:16:07 AM »
I only mentioned modifying a drill bit because if you live in a small town (like I do), you can't buy an end mill.... anywhere....  ::) .... so it's a work-around....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline SILENT SQUIRREL

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #10 on: February 23, 2021, 09:44:57 AM »
I only mentioned modifying a drill bit because if you live in a small town (like I do), you can't buy an end mill.... anywhere....  ::) .... so it's a work-around....

Bob

Bob
I hope you did not take my remark as a criticism.
None intended, of course.

With your skills, knowledge, and experience I'd bet there are work-arounds in your tool box that perform better than specialty tools they replace
Ed

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Offline rsterne

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Re: DISCOVERY VALVE MOD: Angle drilling: HOW??
« Reply #11 on: February 23, 2021, 02:32:09 PM »
You would win that bet....  8)

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).