Drilling accurately

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I want to build the brake on Miller's site: http://millerwelds.com/interests/projects/bending-brake but having problems with drilling the holes for the hinges.I'm usually off by about 0.02 and hope for suggestions to improve the accuracy.I'm using a Martlett/Makita light industrial drill press with a relatively good holesaw and drill at the slowest speed 160 RPM.I also use a center finder in the press to accurately align the piece before drilling.Or would 0.02 tolerance be acceptable in this application?
Reply:.02 Millimeters?Yup
Reply:You using a caliper to measure? I use a tape and never second guess it. But I would venture to say 0.02 in whatever precision you're using would be fine.As far as lining the holes up accurately. If I need absolute precision, I mark where I want my hole, then grab a punch, and hit the center. I let the bit center the piece itself by lightly touching the work piece, clamp it down, and goto town. But that's just me. Someone might have a more profound way of doing it with a drill press.Miller Syncrowave 180SDMillermatic 175
Reply:You are talking about 0.02" off on 5/8" diam?1. I do not know if you even can measure that accurately on such diam...2. If you spent some qualty time and did really precise measurements - it can be just ellipticity of drill / machine...3. I say just finish the press...
Reply:Originally Posted by Burnit.02 Millimeters?
Reply:Have you tried a dial indicator to check for spindle slop?This PDF may be of help:http://www.rvplane.com/pdf/drill_press_tune-up.pdfLast edited by kepe; 08-08-2008 at 08:38 AM.
Reply:0.02 inches. Sorry for disappearing, my broadband is down so I'm posting from my mobile - frustrating.Thanx for the good responses. I'll check that pdf out. Appreciate the encouragement.
Reply:Originally Posted by cassidyI want to build the brake on Miller's site: http://millerwelds.com/interests/projects/bending-brake but having problems with drilling the holes for the hinges.I'm usually off by about 0.02 and hope for suggestions to improve the accuracy.I'm using a Martlett/Makita light industrial drill press with a relatively good holesaw and drill at the slowest speed 160 RPM.****hole saws have inherent runout and cut oversize. Drills, especially a 5/8" dia. drill in 3/16" material, will create an out of round hole.     Hougen rotobroach tools don't--and the spring loaded ejector pin pilots in the center of   the center-punched hole. These tools trepan (machine holes, accurately and fast.I also use a center finder in the press to accurately align the piece before drilling.Or would 0.02 tolerance be acceptable in this application?
Reply:This hinge piece will be welded onto the rest of the frame so an error in placement of that size can be corrected for but you do need the holes to be round and the exact size so the "hinge pin' will contact all sides of the hole and have no excess play. If you don't have access to fancier tools, perhaps drilling undersize a little and carefully enlarging the hole with a file (using prussian blue or similar dye) would give a better fit. Maybe file a piece of the hinge pin (in the drill) undersize a bit to use as a guide for finding high spots as you near the correct diameter.I would use a boring head on my mill, or cut a one-flute cutting tool from the hinge pin stock and case harden it well, then use it in the drill press, or even swage the hole to size with a hardened, tapered pin hammered through a slightly undersized hole.The real hinge pins can be a few thousandths undersize if needed to get the correct clearance in the hole you make.
Reply:If precision drilling is a problem I would consider cutting a precision hinge and pin set off something else, and then welding that on as the hinge. Next question... What's laying around Cape Town that we can cut  hinges off? Bank vault?? Or if you don't have "time" for that... there must be a truck axle shop around; and kingpin bushings are routinely  reamed to fit. How about starting with a truck kingpin and bushing set, and then having the hinge bores reamed to fit? The hinges would definitely be heavy duty, and a precision fit.
Reply:You've given me a few ideas! Thanx.
Reply:Originally Posted by kepeHave you tried a dial indicator to check for spindle slop?This PDF may be of help:http://www.rvplane.com/pdf/drill_press_tune-up.pdf
Reply:Originally Posted by cassidyYou've given me a few ideas! Thanx.
Reply:Donald, he stated that he was using a drill press, not a mill. I assumed that he was saying that he had wobble in his spindle, therefore I gave him accurate information. So, is that funny?
Reply:Of course with the right machine and tooling, anything's a cake walk.But I figured that since the OP was building a brake, resources were limited; that's why I suggested alternates to precision hole cutting; such as cutting a hinge off something else.I was thinking that the hinges would be at least an inch or more thick, I never pictured a brake with such light hinges. Regardless, I think that building one-off hinges from scratch, (especially big ones) is usually a poor use of shop time.I believe that hinge sets of superior quality can be cut off of an old truck or machine, and welded on, easier and faster than could ever be made out of thin soft steel, even with a rota-broach and complete machine shop.  There are just too many alternate sources of cheap half-built hinge parts to make scratch-built practical.Some other sources for nice poor-boy hinge and pin sets are truck spring shackles and their pins, Caterpillar stock parts,  mounted bearings, and don't forget ag tractor hitch pins and their bushings and spherical bearings. When I scrutinize a scrap pile, one of the things I really hate to see go are nice big hinge joints, complete with hard pins and grease fittings.What... That don't bother you?!? Last edited by denrep; 08-09-2008 at 06:48 PM.
Reply:There's two questions here. One is, is a hole within .020 accuracy adequate for this project? The answer to that is snugness of fit is more critical than accuracy from a target of 5/8ths (.625). Snugness of fit will aid greatly in assembly and alignment. We're making a sheet metal brake here, not robotic arms for the space shuttle. You're starting with two small stubs of supposed 5/8th rod of unknown parentage. Maybe even stubs cut from bolts. Measure the rod first. It probably isn't exactly .625 and probably not perfectly round in the eyes of a machinist and purist. Then drill and file a hole as tight as you can get for a tight fit. That'll help a lot when you go to do your button weld to hold the rod stubs in permanentaly. That's the pins. Weld all that to the various pieces of flats, angles and box tubing for the one half of the brake. Now the receiving hole for the pivot needs to be a relatively snug fit sure, but remember you're going to drill a hole in two small tabs, weld those tabs to to multiple pieces of angle and box tubing at dubious degrees of accuracy and placement for the other half of the brake, any .020 inaccuracy is going to be lost in the welds, warpage, distortion and over all assembly of this device. They have included some ingenious placement of threaded stock for thickness adjustment and alignment. The first few bends of oversized material using a metal to metal friction joint with only 3/16th bearing surface and the two hunnerts  tolerance will be long forgotten.The other question is how to go about drilling more accurate holes when accuracy counts.  There are several ways of drilling an accurately sized hole, most of them are spelled more $$$$$.Last edited by Sandy; 08-09-2008 at 06:55 PM.
Reply:Originally Posted by kepeDonald, he stated that he was using a drill press, not a mill. I assumed that he was saying that he had wobble in his spindle, therefore I gave him accurate information. So, is that funny?
Reply:THANKS BLACKBIRD ! I have always wanted to learn more about machining.I would need one more lifetime.AWS certified welding inspectorAWS certified welder
Reply:Donald, thats cool. I was just trying to give him the best info I could with the tool he stated he was using. I know quite a bit about drill presses because I restore old line-shaft and WWII vintage drill presses, etc. and I have to " tune" them up....they can be quite accurate when setup correctly.
Reply:Kepe You are right about using a dial indicator to check runout on a drill press, We do it to all our drill presses at work to make sure they are a s true as they can be. Anyone who has a drill press should check it and make sure it is as true as it can be. What is the sense in using a drill press if it isn't going to give you good results.Donald Branscom You can very easily get .020 accuacy from a drill press. You do not need a mill for that kind of accuracy, if we was talking about .002 then you would need a mill.If you have not had good luck with a drill press then try reading the PDF file that Kepe posted it is very good. There are also plenty of other articles on the net that will teach you how to make your drill press true.
Reply:The chuck does not wiggle when shaken side to side even with the quill fully extended. Time for me to get a dial indicator then.Sandy - I came more or less to your conclusion.Thanx to all - it was very informative.