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Drill press technique

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Drill press technique

Unread postAuthor: daccel » Tue Jun 16, 2009 11:50 pm

I'm trying to drill a rod out to the shape below, and having trouble keeping the bit perfectly centered on the long one. You can see how far off it is after 4". And the problem will be amplified when I make the wider pass.

I realized after I should have tilted the table 90 degrees, and clamped it along the length. But any other tips for making a more precise hole, or how to line it up with the bit? Should I drill the wide or narrow part first?
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Unread postAuthor: Technician1002 » Wed Jun 17, 2009 12:08 am

As strange as it sounds, chuck the rod and clamp the bit. When the rod is true it tends to be self centering. Lathe work does this all the time. Instead of a drill bit, a boreing tool works better at keeping centered on this type of drilling.

http://www.truetex.com/boring.htm

A good how to is here for use on a lathe. Adapting to a drill press can be done.

http://www.nmri.go.jp/eng/khirata/metalwork/lathe/drill/index_e.html
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Unread postAuthor: psycix » Wed Jun 17, 2009 3:56 am

You will really need to go 100% straight, or you will have a weak spot in the wall. You should really do this on a lathe (or mill), but if you don't have access to one, it will be very hard to keep it centered.
I dont know what kind of pressure you are planning to put in, but make sure that you know there are no thin spots in the wall!
Dont make the walls too thin if you are unsure of your capabilities.
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Unread postAuthor: Technician1002 » Wed Jun 17, 2009 4:07 am

psycix wrote:You will really need to go 100% straight, or you will have a weak spot in the wall. You should really do this on a lathe (or mill), but if you don't have access to one, it will be very hard to keep it centered.
I dont know what kind of pressure you are planning to put in, but make sure that you know there are no thin spots in the wall!
Dont make the walls too thin if you are unsure of your capabilities.


If he chucks the valve body in the drill press chuck and use a boring bar, it should be difficult to get off center. It may have chatter and need smoothed with a twist bit, but the initial bore should be true if it is chucked straight.

The other option is to use an oversize piece of round stock and drill it small (possibly off center) , tap it, and turn the outside down to size on the centerline of the hole. When that is done, the hole can be bored out larger to the final size on the pilot hole.

I did that with the valve core of the 2 inch QDV cannon. I had a squareish block. I bored it, threaded it and chucked it in the drill press and cut the outside to size and shape, then bored the hole larger for the trigger rod.
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Unread postAuthor: far_cry » Wed Jun 17, 2009 8:44 am

YOU will need a lathe mate
you cant make it without lathe
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Unread postAuthor: Technician1002 » Wed Jun 17, 2009 10:01 am

far_cry wrote:YOU will need a lathe mate
you cant make it without lathe


Good point. It works barely for softer stuff like HDPE, but solid metal would be a problem. It may work well enough to center and drill the pilot for a larger drill bit. May be worth a try to get the center hole centered. Watch the bit as the metal turns. If it wiggles, it's off center. If it stays still, it's centered.
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Unread postAuthor: daberno123 » Wed Jun 17, 2009 10:23 am

What kind of vise are you using? Just a regular drill press vice or a machinist vise? With a machinist vise you can adjust it until you know you're starting at the center.

I would suggest switching from round stock to square stock instead. Your idea of turning the table 90 degrees and clamping lengthwise is a good one, but square stock would provide more surface area to contact the sides of the vise, allowing less vibration.

Tech's suggestion of chucking the round stock and clamping the drill bit is good, but you're probably going to have just as much trouble keeping the bit straight in the vise as you are with the round stock.

If you don't mind, what kind of drill press are you using? I've been looking around for one and any info would be appreciated.
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Unread postAuthor: btrettel » Wed Jun 17, 2009 10:23 am

Without a lathe it'd be easiest to start with a tube like your long segment, fill in the end with epoxy, epoxy putty, or something else, and then finish the end. I don't know the specifics of your plan so the filler may not be appropriate.
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Unread postAuthor: Gaderelguitarist » Wed Jun 17, 2009 11:30 am

Always drill the more narrow part first! This ensures that the two different diameter holes are true to one centerline.

Theres a thing called a self centering chuck for a lathe. One will run you a couple hundred dollars, but they ensure that the piece is centered for whatever you're doing.
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Unread postAuthor: Technician1002 » Wed Jun 17, 2009 11:54 am

daberno123 wrote:What kind of vise are you using? Just a regular drill press vice or a machinist vise? With a machinist vise you can adjust it until you know you're starting at the center.

I would suggest switching from round stock to square stock instead. Your idea of turning the table 90 degrees and clamping lengthwise is a good one, but square stock would provide more surface area to contact the sides of the vise, allowing less vibration.

Tech's suggestion of chucking the round stock and clamping the drill bit is good, but you're probably going to have just as much trouble keeping the bit straight in the vise as you are with the round stock.

If you don't mind, what kind of drill press are you using? I've been looking around for one and any info would be appreciated.


I would use a cross slide drill press vise holding a Jacobs chuck with a custom double d flat shank for secure mounting.

http://www.amazon.com/Universal-Cross-Slide-Drill-Press/dp/B000II2KDO

http://www.sears.com/shc/s/p_10153_12605_00929849000P?vName=Tools&cName=PowerToolAccessories&sName=Lathes&psid=FROOGLE01&sid=IDx20070921x00003a
Cut flats on a spare taper to fit the vise.
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Unread postAuthor: psycix » Wed Jun 17, 2009 2:19 pm

Maybe you should look into making the "complicated" part (on the left in the diagram) out of massive material, and the long, hollow part out of a tube which you connect with bolts, epoxy, threads, oring, whatever.
That way you do not have to worry about going off-center and having variable wall thickness.
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Unread postAuthor: jimmy101 » Wed Jun 17, 2009 3:01 pm

To get this to work with a drill press is going to be tricky. That looks like a piece of aluminum so you might be able to do.

Definitely use Tech's suggestion and chuck the stock, not the bit. That'll put a lot more metal in the moving jaw.

I suspect you'll need a pair of bushings and/or bearings to keep everything straight and aligned. One bushing that holds the unsupported end of the stock in the correct place. Another that supports the drill bit near the point where it actually enters the tube. This second support will have to moved occasionally as the bit enters the stock. The second support doesn't need to be a bearing since the bit isn't turning. The first really should be a bearing since the stock is turning.

Psycix suggestion is also very good and completely avoids the problem of drilling a long hole through the stock.
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Unread postAuthor: D_Hall » Wed Jun 17, 2009 6:39 pm

There are special bits made for drilling such holes. I don't know if it's the name of the bit or not, but the process is refered to as "gun drilling" (so you may try googling that).
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Unread postAuthor: Gippeto » Wed Jun 17, 2009 11:40 pm

Although brettel, and psysix offer good and workable solutions to making the part, I think I'll go with far cry on this one. You need a lathe.

Even very minor alignment errors will add up over 4"

Is your stock 5/8" or 3/4"? Some drill presses do have a 5/8" chuck, but very few home drill presses are going to be able to chuck 3/4" material.

If you wish, pm me with a dimensioned drawing and we'll talk.
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Unread postAuthor: daccel » Thu Jun 18, 2009 12:27 am

I smell a challenge :D.

Wow lots to respond to, sorry if I leave something out.

I know I could use epoxy or separate parts, but I wanted to use a solid piece due to strength and size restrictions. I initially was going to sleeve tube and epoxy it in place, but needed a different size for the piston, and just wanted to do it right. I will probably still sleeve the thin walled portion with 1/2" copper couplers (it is 5/8 aluminum stock).

There was a lot of good suggestions here, but I thought I'd try the simplest with what I had at hand, and work up from there. I don't know what they are from, but my dad gave me these two short sections of thick metal tube from work a while back, and they happen to have a 5/8 inside diameter, so I was able to use them, with several diminishing sizes of tube inside for the drill bit, as bushings (correct term?). One will also form the outside of the valve eventually.

I left the bit (3/8") in the chuck, because it is only 1/2". The tube bushing kept riding out, and I didn't have any blocking under the stock, just held it by hand, but slowly managed to make it through. Shortened the bore hole to 3.5".

I think it may be as good as I will get without buying more stuff. It's off by .004" at the start and .014" at the cross hole. I suspect there may have been some luck involved :P. Still have to drill the wider pass, because it got too late (no I don't have a curfew, I just don't want to piss off my neighbours - joys of apartment living), so we'll see.

I'm still digesting all the suggestions and new stuff to plug into google, I saw some interesting sites earlier. I will post up some links later for future reference, or if this doesn't pan out on the second pass.
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