Drill a very long 1/16" hole without breaking bit?

[Rocketcaver]

I'm yet another noobie, starting on Elmer's #19 Standby. I have the frame (aluminum) milled to shape and all the holes layed out. If you are familiar with this little engine, you will recall that it gets a rather long 1/16" hole drilled down the length of the frame into the shaft area for the valving, and that makes me a little nervous. I haven't tried this yet, but have not had much luck drilling long small holes in the past. Such ventures usually leave me cursing at a bit broken off inside the hole. I plan to do the job on my mini mill, with the frame clamped securely in the vise, with liberal applications of cutting fluid along the way. I would appreciate any advice on how to avoid the accursed broken bit.

 

[Shopguy]

Make sure you are turning the drill fast enough, probably the max speed on your mill. Peck drill the hole, that is apply pressure to the drill so it cuts just a small amount,say a sixteenth of an inch then withdraw the drill to allow the swarf to come off the bit. As you get deeper the amount reduce amount of cutting between with drawing the bit. If the cuttings stick to the drill stop and remove them before proceeding. Aluminium can be sticky stuff and can at times really get stuck in the flutes of the drill, especially drills not specifically sharpened for drilling aluminium.
Don't hurry.
Regards
Ernie J

 

[champ2run]

Dear Rocketcaver: My way (which may not be the best but it always works for me) is as follows. Securly fasten down the part to be drilled. Use a spotting drill or center drill to accurately dimple the hole's exact location. Without moving the table, insert a new drill (or a correctly re-sharpened one) into the chuck. Using cutting/lubrication fluid begin to gently drill the hole; use just enough load on the drill to keep it cutting rather than rubbing.
Now the important bit. Once you are about 1/4" to 3/8" into the hole extract the drill completely, brush off all swarf, relubricate and re-enter the hole. drill for about 1/16" and then extract, brush and re-enter. Keep drilling in small increments, brushing away all swarf and re-lubricating. It is boring, it takes time, but you won't break a good quality drill doing it this way. Here in the USA I believe they call it "pecking". Good luck and best wishes. Ted.

 

[GWRdriver]

One word: Patience. A few years ago I had two 1/16" x 7/8" holes to drill through a bronze block (for steam passages.) The fist hole went through easily and was perfectly located. The second hole wandered by 1/16"+ and broke through another passage ruining the block.

I started the process with a brand new, 1st quality, drill bit and began drilling at fairly high rpm using a tiny squirt of cutting fluid (Tap-Magic) each time I withdrew the drill, which was often, after no more than 3/32" or so. So far so good.

What I did not do on the second hole, which I should have done, was first to start with a new drill bit, but what ultimately messed me up was this. The first hole went so well that I assumed I could go a bit longer between withdrawals, that is, drill the hole faster, which I could. What I did not know was that the almost imperceptible difference in frequency of withdrawal and pressure on the drill bit in the second hole caused the bit to wander just enough to ruin the job. Aluminum is going to make for more difficult drilling because of its tendency to load up the bit. That will mean a greater frequency of withdrawal to clear chips. Take it very slow, use a new bit, lubricate and withdraw often. Good luck.

 

[lensman57]

Hi,

I built this engine last year, I think that it was my second engine. As I recall I indicated the part while upright and then drill 2/3 of way down by using the lever on my X1 mill, I used a lot of lubricant, WD40, and frequently withdrew the drill to remove the swarf that will inevitably stick to the tip. I then turned the part upside down and indicated again making sure that the part was true and vertical and then drilled from this end. to my relief the holes met up excatly on axis. This may not be the best way of doing this but it worked for me.

Regards,

A.G

 

[Rocketcaver]

It looks like the common theme here is "peck drilling". Actually I have done what amounts to peck drilling, but my "pecks" are more like "lunges", that's what breaks the bit I suppose. I need lo lighten up and take smaller bites.
Also, hadn't thought about starting with a brand new bit. I'll have to order those tiny screws anyway, I might as well order a few new bits while I'm at it.
Drill speed... full speed on this minimill is really wound up, MicroMark claims top speed is 2500 rpm. I tend not to run it much more than half speed, maybe that's part of my problem too.
Thanks very much everyone.

 

[Inky Engines]

Lots of good advice above. I would just note that this hole is too deep for a standard jobber drill ... I used a long series drill with no problems.

Kind regards

Geoff at Inky Engines

 

[MuellerNick]

What is "rather long" or "very long" for a 1.6 mm drill in mm (or inches)?

I do have a 4 mm drill that is 280 mm long (flutes go 190 mm). Would that be "rather", "quite", "very", "extra" or "extremely" long?


Nick

 

[Rocketcaver]

This particular "rather long" hole is in the neighborhood of 1 1/2".

 

[MuellerNick]

This particular "rather long" hole is in the neighborhood of 1 1/2".

So that is about 24 * D (that's how drilling depth is qualified).
You need a special drill for that, a deep-hole drill, also called crank-shaft drills. "Common" drills only go 5 *D (you can abuse them to 10 * D).
Start with centering, then a normal drill 5 * D deep, than switch to the deep hole drill.


Nick

 

[Mosey]

What is "rather long" or "very long" for a 1.6 mm drill in mm (or inches)?

I do have a 4 mm drill that is 280 mm long (flutes go 190 mm). Would that be "rather", "quite", "very", "extra" or "extremely" long?


Nick

According to my chart, that is officially "somewhat" deep.

 

[GWRdriver]

Yes, What Nick said, about 5xD deep. What I did with my deep holes was to make them a series of 1-2xD plunges. I got over-confident, exceeded that, and didn't do it slowly enough on the second one, resulting in ruin. I had a good friend (and mentor - now deceased) who drilled a 1/16" x 7.25" long hole in a model engine camshaft. I didn't watch him do it, that took days, but I saw it in-process, and the final product. He just simply pecked and cleared until he got it through, using an extra-long "aircraft" bit. He drilled half-way through from one side, reversed the shaft, and drilled back through from the other side. The holes aligned well enough that he could pass a 1/16" drill rod through the hole. If you compute the recommended cutter tip FPM (feet per minute) for very small drills relative to the material being cut you get really crazy rpm numbers, like 20,000prm. Few of us have that capability. My old Rockwell drill press (15") is capable of maybe 4500rpm tops and in many many years I have needed to use that speed less than a dozen times. (Neither of us like going that fast.)

 

[Ken I]

All good advice above - use new good quality drills - start with a spotting drill, follow with jobber drill and then a long series drill.
Don't move anything, rigid set up, plenty lubricant and correct rpm - probably max out your mill. A good start is essential to not having the drill wander which apart from the accuracy also prompts drill breakage.

If you are using resharpened drills the lips must be dead equal or it will also induce some drunken wandering of the hole.

"Pecks" need to be progressively shallower with each peck as the hole gets deeper.
Note how the swarf is packing up in the flutes with each peck - if its starting to become swarf bound you need to go less per peck.
Some sort of indicator helps (DRO is nice) so that you don't go lunging into the bottom of the hole or use an adjustable stop to back up for each increment.

Listen to your machine (or use an ammeter) any sign of "labouring" - back out quick.

My personal record is 67mm with 1.5mm (45D) in steel and 148mm with a 4mm drill (37D) in Aluminium.

Be very carefull of work hardening steels (some stainless etc) as you cannot afford to rub when resuming drillling after each peck - must attack at feed rate and back away sharply - hesitate and you're lost.

And has been mentioned - Patience.

Ken

 

[Rocketcaver]

Brand new long bit, lots of Tap Magic, full speed on the mini-mill, and dozens of short pecks did the trick. I made the hole last night with no problems. It took a while, but worked like a champ.
Thanks everyone for all the good advice. I got that passageway drilled then did the rest of the holes on the frame before calling it a night. While this was going on I also reformatted the hard drive and re-installed Windows XP Home Edition on my shop computer. It was a full evening, but I got a lot accomplished.

 

[cfellows]

All these suggestions are good ones... Use a new or freshly sharpened bit, withdraw the spinning bit frequently from the hole to clear the cuttings and lubricate the bit. The real key is, only drill about 1/16 - 3/32 at time.

To make the process a little faster, I use a small, open container of oil with an acid brush (or other stiff bristled brush). I withdraw the bit from the work, dip the brush in oil and use it to clear the cuttings and lubricate the bit at the same time, without stopping the drill.

Chuck

 

[Rocketcaver]

Good idea. I was using a small acid brush to clear away the cuttings, but had to stop the bit occasionally to manually remove stubborn chips from the flutes. I was amazed at the end of the process, the end of the bit still looked almost new.

 

[GWRdriver]

Good job. Congratulations.