Basic Operation Question

[gangel99]

I have a general question about what is the best order for drilling operations when you do not have a DRO.

In this specific case I need to drill a line of four, 3/8" holes in 1" thick steel. The operations I am doing are: 1)spot drill 2)pilot hole - about 1/8" 3) drill full hole size 4) chamfer. I have to do this on four pieces of steel.

I first thought it was better to do all the spot drilling, then the pilots, etc. so I would only have four tool changes. Without a DRO, however, I have to get on center with every operation and it seems like it would be more efficient to keep the center on each hole, and do all the tool changes and operations for the hole, and then move to the next one.

The location of the holes does not have to be very accurate but the chamfer in particular has to be on center.

Sorry this is so basic - I have not found an answer in the books I have and I am sure the answer lies in experience. I have thought of some kind of jig but I am not sure how to make it, and in the end it is only four pieces and sixteen holes.

[mechanicalmagic]

If it were me, it would depend on IF I could do all the operations without moving the knee.
Each set of four holes is a different setup, I would not stack them.
If all tools fit with one knee position, then I would set one hole, and do all operations, on one hole. Then move to the next hole.
However, if the knee has to be moved, then spot, pilot on all holes, reset knee, drill, reset knee and countersink.

Another method, when tolerances are loose, is to set a stop on the mill vise. Insert part #1, spot drill, remove part #1, insert part #2, spot drill..(4x). Move to hole #2, spot..... Often changing parts can be done quicker than swapping tools. At the risk of a chip getting in the way, possibly ruining a part.

Dave J.

[BadDog]

What are you using to drill? A mill? Or at least a decent X-Y table? If so, the dials should easily repeat well enough for this. As suggested, assuming a suitable shaped part, set a stop in the vise (or simple locating fixture if needed), set your "line" on the y-axis and lock. Now pick up whatever feature (perhaps even the stop) and crank through the 4 hole x locations. Go through all 4 holes on 4 pieces (using just the x-axis) to spot. Swap tools and repeat until done. And also as suggested, just make sure you don't get a chip throwing things off, and always feed the same way to avoid back-lash issues.

[gangel99]

Dave, Russ - thanks for your help. - I knew there was a better way

I am using a mill-drill with the head on a dovetail (RF-45). I do not have to move the head - only the quill and it makes total sense to swap parts rather than tooling, or move the table. Do all the operations on hole #1 on four parts, then move the table to hole #2 and repeat.

Although I could rig up a stop with my clamp kit you have inspired me to make a vise stop.

[david5605]

I have drilled a bunch of 1/2" diameter holes in 1/4" plate steel in one shot with the 1/2" drill in an ordinary drill press.

I have a RF45 clone and would not hesitate to drill the 3/8" holes in one shot (no spot, no pilot). If I could stack them , I'd stack them. I just use ordinary motor oil (used) as a lube. Squirt as I go.

Based on how deep the chamfer has to go I'd just set up a stop to stop the part from spinning and let the chamfer drill self center. No clamping necessary.

[Napper]

I agree with Mechanicalmagic except I would skip the use of a pilot drill. It is not needed. A 1/8 dia. drill thru 1 inch thick material is easily broken. So just spot or preferably center drill. then drill the 3/8 hole. Another tip place two small springs between the parallels to keep them in place while you repeatedly open and close the vise.

[seal killer]

gangel99--

Gee. These guys know everything and everything I learned was from these guys. So, how could I offer different advice?

I hesitate to do so, BUT if you have a rigid setup then my experience tells me that the best way to drill the holes is to . . .

1. Locate the left edge precisely. (This assumes the holes can be milled along the X axis.)

2. Move to the first hole location.

3. Spot drill.

4. Move to the next hole.

5. Repeat steps 3 and 4 until spot drilling is complete.

6. Change drill bits. Since they are 3/8" holes, I would use a 3/16" drill bit as a step drill on the way to 3/8".

7. Locate the left edge precisely.

8. Move to the first hole location.

9. Drill to depth.

10. Move to the next hole.

11. Repeat steps 9 and 10 until step drilling is complete.

12. Change drill bits. (Insert the 3/8" drill bit for finish drilling.)

13. Locate the left edge precisely.

14. Drill to depth.

15. Move to the next hole.

16. Repeat steps 14 and 15 until finish drilling is complete.

Repeat all the above for each of the four workpieces.

IMPORTANT: Trust the dials. Obviously, the center of each hole is a precise distance from the center of the preceding hole. Turn the X axis dial that exact amount and you will find the drill bit precisely postioned over the center of the spot or hole. Do not turn the dial in the opposite direction! If you do, then you have lost your ability to precisely locate the next hole due to backlash. In this case, return to the left edge and locate it precisely and then simply turn the X axis dial to the hole needing attention. No problem. Trust the dials, gangel99, trust the dials.

This worked for me EXCEEDINGLY well. However, there may be differences between what you are doing and what I did. You are making four holes in four workpieces. I made 50 holes in a single workpiece. Additionally, you are working with steel while I worked with aluminum. Although I cannot see where any of that might make a difference, I will bow to the wisdom of those that are experienced.

--Bill
ps Create a TEST piece to refine your practice of the technique.

[seal killer]

gangel99--

A FIX to my post above.

Where I say "left edge" I should have written it so that you understood the position I meant was the 0,0 location. Ideally, this would be located at the top left hand corner of your workpiece. Once located, you turn both the y axis dial and the x axis dial to locate the position of the first hole, and then the x axis dial as I described in the post.

If you turn the y axis dial in the opposite direction, you will have to re-find the y axis zero. Usually this means refinding the x axis zero, as well.

If you turn the x axis dial in the opposite direction, you can simply refind the left edge of the workpiece and turn the x axis dial until you reach the correct hole position.

Here is an example of how this works. The hole ID is so close to the OD of the cartridges that it takes a little finger push to finally seat the cartridge due to trapped air pressure.

9mm Ornamental Cartridge Box

--Bill

[Willy B]

You ask "How would you do it?"

I would center drill, then drill the hole with a 3/8" drill , then chamfer, then on to the next hole. Its personal. I find that I am much more likely to screw up while relocating the part than swapping out tools. So I keep relocation to a minimum. The holes do not have to be precise, so no need for all the step drilling. I find that a hole started without some sort of guidance might end up most anywhere. I have also found that when using center drills to max depth, there is an increased chance of twisting off the tip.

Speaking of pilot drilling, a tip that has been handed down to me: A good sized pilot drill is one that will lay in the flute of the larger drill.

As a machinist, you evolve to where you do things in a manner that works for you. Something like this, there really is no right or wrong way.

Bill

[Inspector]

Any reason not to use the spot drill and go in far enough to create the chamfer, then drill with the 3/8? Then you only need to do 2 tools per hole.

Reason I ask is I've seen it done that way at work when they make fixtures etc. When the hole is to be threaded, the tap follows. So 3 tools in that case.

Pete

[Lew Hartswick]

Any reason not to use the spot drill and go in far enough to create the chamfer, then drill with the 3/8? Then you only need to do 2 tools per hole.

Reason I ask is I've seen it done that way at work when they make fixtures etc. When the hole is to be threaded, the tap follows. So 3 tools in that case.

Pete

How big do "spoting" bits come? That sounds like a winner. Of course the
chamfer is 118 deg rather than 90 but who is gonna see that. :-)
...lew...

[toastydeath]

Any reason not to use the spot drill and go in far enough to create the chamfer, then drill with the 3/8? Then you only need to do 2 tools per hole.

Reason I ask is I've seen it done that way at work when they make fixtures etc. When the hole is to be threaded, the tap follows. So 3 tools in that case.

Pete

This, proverbially, is how I roll.

Get a bright light and some calipers, and eyeball the OD. It may be obvious, but desired chamfer *2 + hole diameter.

I have 1-1/2", 90 degree spotting bits, so I'm pretty sure any size a HSM would need is available.