How to Drill Accuretly

[oskar270]

I’m building a cnc mill (36”x24”x12” and this is the first time I work with metals (aluminum). As you can see from the pics in photobucket I have the sliding blocks on the rails which I have to attach to my cnc and I have a hard time aligning the holes on my aluminum members for drilling.

http://s285.photobucket.com/albums/l...inear%20Rails/

I wonder if there is a method / jig to make this process easier. I know that there are these things you put in the holes to transfer the pattern but the sliding blocks have 5mm holes and I can’t find those things in metric

I do have the drawing / dimensions of the blocks but even with that I can’t get it ok. I guess even the angle of the scriber has an affect

How would you do the drilling?

[Dr Stan]

How would you do the drilling?

It sounds like you're trying to drill your holes in a drill press. Is this correct?

For any real accuracy you need a milling machine or even better a jig borer.

[TGTool]

You can easily make a transfer punch exactly the size you need from drill rod. Since it will be for short time use you might get away without hardening it at all, or at most only the point needs hardening. The back end may well mushroom from use but it won't distort enough to be unusable for the number of holes you need I would expect.

[Boucher]

When ENCO has their transfer punches on sale I buy them for a cheap assortment of working stock. You could easily take a slightly oversize one and turn it to the desired diameter.

[elf]

I'd start here: http://www.gadgetbuilder.com/OpticalPunch.html or just buy one: http://www.grizzly.com/products/H5781

Then use something like this: http://www.ebay.com/itm/Driil-Bushin...f82dd7&vxp=mtr

[koda2]

transfer screws

For years I tried to do accurate work with nothing but a hand drill and a drill press. Extremely frustrating but I gathered a bunch of tricks over the years that helped.

It looks like you are trying to match 8 threaded holes to a plate. You can make transfer punches out of screws or bolts.

Get a bunch of 5 mm or whatever bolts, cut off the heads and have some one with a lathe turn some points on the threaded portion like so:



They would have to be much shorter for blind holes and be careful not to thread them too tight or you won't get them out. Use some Dykem or transfer dye on the plate you want the holes drilled in. If you don't have the real dye, use a black Sharpie and color the plate. It will work and is easily removed off aluminum with isopropyl alcohol.

Put the two parts together and tap lightly to score the plate. The smaller the hole or mark, the better.

Once the plate has been marked, use a spud bit or any thing similar that will show you where the exact point to drill is:



A magnifying lens will help you get the tip of the bit exactly where the hole is supposed to be. Lock the plate in place on the drill press, and progressively drill up to the proper size, starting with a very small drill bit and go slow. Drill bits will wander,even on a drill press if you don't have a spotted hole, or center drill to make it stay in place.

You should get a transfer of holes to match your pattern. From the looks of the design a slightly oversize hole would be okay anyway, so that there would be no binding of the blocks as they traveled.

DA
P.S. I use this homemade spud bit all the time for semi-precision work and it does a great job. Got it from Guy Lautard's books

[Arcane]

You can easily make a transfer punch exactly the size you need from drill rod. Since it will be for short time use you might get away without hardening it at all, or at most only the point needs hardening. The back end may well mushroom from use but it won't distort enough to be unusable for the number of holes you need I would expect.

Certainly works for some of the cheap versions of those tools I've seen in Princess Auto!

[Paul Alciatore]

Certainly the best way to drill accurate holes is with a mill-drill or an even more accurate machine. But I doubt that you have any such so...

Here is my approach to manually drilling accurate holes. It starts with an accurate layout first. First you apply layout die or just cover the area with magic marker. You will need a sharp scribe: the sharper the better.

There are many ways to layout: surface plate and height gauge, calipers, square that is set using calipers, and many, many more. But the hole locations will never be any better than the layout.

Next I use a prick punch to make a small dimple at the intersection of the layout lines. I use a 10X magnifier to place the point of the prick punch directly on that intersection. Some do this by feel. I then check that position to see if it is dead center of off a bit. It is usually a small bit off. If it is off by a lot, I just do a better one.

Next is a center punch. It must have a good, sharp tip. That tip is located in the mark of the prick punch by feel. Now, I remember what direction the prick punch was off by and I tilt the center punch to move the punch mark back to the intersection. I give it a light tap with a small hammer or other available object. I inspect the result under 10X magnification and again note which direction it is off in. A second punch with the center punch, again leaning in the direction to make a correction and I am usually very close to dead on.

Now I must actually drill the hole on the punch mark. This is not easy because drills can wander. Many like to use spotting drills to start the hole, but I disagree. I feel that the largest mistake I can make in locating a hole is the radius of the drill being used or, most often, a fraction of that radius. So I want to start the hole with a drill that is both small and rigid: sounds like two contradictory requirements. Spotting drills are rigid because they are short, but they are usually quite large with the smallest one usually available being 1/4". The web of such a drill is too big for accuracy measured in thousandths.

A center drill has a small pilot section and that small pilot is just what the doctor ordered. It will have an even smaller web and that will certainly stay within the punch mark. So we are down to just a few thousandths of error here. I will drill down until the larger section of the center drill just starts to enter the hole. This leaves a small, 60 degree cone and a very small pilot hole.

Now if the hole is small, like 1/16" or 1/8" or so, I will drill with the final drill. It will follow the pilot hole until it's full diameter is fully into the hole and then there will be very little wandering. If the hole is larger, I will use an intermediate drill that is about the size of the web of the final drill size. This drill will go down at least far enough to allow the final drill to fully engage before reaching that depth. The intermediate drill will follow the pilot hole and the final drill will follow the intermediate. There will be very little deviation unless a hard spot is hit while drilling.

That is how I can manually drill accurate holes. It is not fast. But it can be very accurate. Perhaps +/- 0.002" or so, depending on the care you use at each step.

[Jaakko Fagerlund]

You can make transfer punches out of screws or bolts.

Get a bunch of 5 mm or whatever bolts, cut off the heads and have some one with a lathe turn some points on the threaded portion like so:

http://pages.suddenlink.net/tismuoi9/transfer.jpg

Have used this trick more than I can count, but you don't need a lathe. Just chuck the screw in a cordless drill and head to the bench grinder. In the OP case he/she needs M5 screws (or is it 5 mm hole, which would make it M6) and basically not much accuracy, as they are screw holes.

Just insert the modified screws partway in the block, lay the block on top of your plate and tap/whack with a rubber mallet to get your marks for drilling and drill 6 mm holes for M5 screws or 7 mm for M6 screws. They are after all screw holes, not alignment pins so a clearance hole is all that is needed.

[Bob Fisher]

IF, you have a way to accurately layout the hole positions, as has been mentioned, an optical center punch is the very best for that sort of center punching. Starting a drill in a located punch is another matter however.I would use a center drill to start,and follow with a larger size. A large plate is difficult to center properly on a drill press. If you can manage to clamp the parts together, you can spot the holes with a drill that fits. If you are using 5mm screws in a 5mm hole, there is not much room for error. Bob.

[rohart]

My way is to use two punches, a sharp light punch, a solid centre punch, and a good scale and a magnifier.

First you measure your existing hole centres, so you know exactly what you're aiming at. Then you use the ruler and make very light punch marks for your first estimate of your new holes. From then on, you use the ruler and the magnifier and you adjust your marks, making then deeper each time, until they are spot on. Then centre punch progressively.

After centre punching, hammer flat and centre punch again. A small drill can work out of the raised edge crater of a centre punch, but if the edges are level with the surface it can't escape and has to drill true.

Remember you can correct at every stage, even if the first drill hole is off. When you start drilling, just spot drill all holes a 1/16th deep. Then back to the bench to check your positions with the scale and the magnifier.

If a hole is off, go back to the drill and hold the part up at an angle to the table so the drill cuts the hole in the direction of 'correct' for another 1/16th or so. Then go vertical again and the hole will have moved to correct itself.

One advantage of a mill is that if you do drill a hole off its mark you can use an end mill instead of the next drill size, and move the hole.

[elf]

#124 in this thread shows how to make and use a transfer punch: http://madmodder.net/index.php?topic=6037.100

[ak95xj]

On a drill press I like to leave the part loosely clamped ..I believe the drill pulls the part into center thru the center punch mark....this is on the first hole/pilot hole.I then carefully clamp it down after that..