PowerPro Reverse drilling

[keakap]

Nothing amazing here, just a comment on a 'new' use (for me) for the PP in drill Press mode and using Reverse rotation.

I had to make a gasket for my old motorcycle and it had to be accurate. I decided to use the "Part" as a template and drill the bolt clearance holes on the D-P.
First problem: the 'part' is aluminum. I did not want to enlarge or mis-shape the holes in it as I used them to locate my drill bit, which was a Forstner of precise matching size and extreme sharpness.
Second prob: to keep the rig from becoming annoyingly complex I wanted to drill the gasket material in "the open", yet the available drill bits tended to make sloppy holes under normal operation.

Solution was to run the D-P at 250 rpm and in Reverse. This allowed moving the Object by hand while lowering the drill bit so as to get it in the hole without marking up or cutting the aluminum, then once positioned and held firm proceeding drilling thru the gasket material underneath to it's thickness Plus ~~ 1/32", which had been determined to be the ultimate setup for clean holes with complete separation. (For anyone not familiar with gasket material of this type, imagine about 40 or 50 layers of highly compressed toilet tissue. The only thing that'll cut cleanly through it is yesterday's baked beans.)

Sounds like much ado about nothing, but it was an easy task as it was performed, and after some very careful knife work on the gasket sheet the result is a nearly perfect gasket, almost indistinguishable from the New.

I've made gaskets before and never had it so easy.

Forstners in difficult materials, and Reverse rotation. LOVE it!

not to mention the 'humongous' & solid workbench I had to slide that slab of plywood backing around on while drilling (SS Main Table)

[rjent]

Outstanding! I am amazed with what my PP can do .... I love it!

[JPG]

Lower the bit 'into the aluminum hole', tighten the quill lock, clamp the workpiece, then turn the bit 'on', loosen the quill and 'drill'.

[dusty]

OKAY, I understand what you did but I am at a lose to understand why. What does reverse drilling do for you that is not done normally?

[reible]

OKAY, I understand what you did but I am at a lose to understand why. What does reverse drilling do for you that is not done normally?

I'm with Dusty on this.

Perhaps a picture of the bit you used would help. I have several Fostener bits sets and I believe many other style exist so I'm thinking perhaps "we" might have things with the same name but don't look alike???

You know the saying a picture is worth a very long post.

Ed

[JPG]

My guess is that the back side of the spurs did not 'dig', but cut the gasket material anyway.

Then there is the possibility that that they were brad point or auger bits.

I use a punch if holes are small enough.

[keakap]

Lower the bit 'into the aluminum hole', tighten the quill lock, clamp the workpiece, then turn the bit 'on', loosen the quill and 'drill'.

Indeed. If there had been even a smidgen of trouble handling the "workpiece" (consisting of a 12" x 14" x 3/4 slab o plywood, the gasket sheet- 7 x 11 x .012~, the "template"- 6.5 x 10 x 2.5~) the procedure would have been exactly as you describe. With good fortune and extreme (tho comfortable) care all went well. I believe I was having a "good day".

And by the way, doing it exactly a-y-d is about the most sure, accurate, smooth, safe and certain way I can imagine without some more really heavy duty machinery brought in to the shop. What a joy.

{N.B.: one of the reasons for going 'live' as it were, was, again, to avoid undue complexity, and having the 'float' allowed me to proceed without removing static quill runout (please bear with my non-engineer-type langwitch). I instead used the simple device of hooking a finger behind the extended quill thus manually de-slopifying the fore-and-aft.

[keakap]

OKAY, I understand what you did but I am at a lose to understand why. What does reverse drilling do for you that is not done normally?

[That's funny- I never noticed that Strategic Air patch before. Woke up a few snoozing memory cells. I was in SAC and TAC at one time or n'other.]

Anyhoo, the reverse drill thing, imho: the bit I decided to use- a Porter-Cable Forstner style, 1/4", was the best I had, for length, diameter, configuration, runout and sharpness. It does a particularly good job in some materials because of (I think) the extra cutting 'edge' provided by an additional 'slot' in the cutting perimeter. Normally with small Forstner, Forstner-like and brad bits I've seen there are two openings in the cutting circle, where the scrapers are. (Sorry, the terminology escapes me, but it isn't all that complicated.)

Then with this one, there is another opening in the 'rim' between the normal openings. {If the edges of these openings were teeth on a saw blade you'd have a 4-toothed blade.}

Running in reverse just allows the rim to "ease" into the cut, and it does so 4 times per revolution, not two. Forward, contact is somewhat more aggressive.
In other words, as far as the gasket material is concerned I get a smoother cut running in reverse. The material is well supported on its backside but there's nothing holding it down AT the point of contact except the bit.

Bringing in the magnifying glass a bit closer, we see the bits rim enter the template hole, partially guided by the finger behind the quill; at this point the bit is spinning inside the hole and there is barely more than 1/1000" clearance (actually less on some of 'em when I started) to the hole side; quill finger removed. With that clearance- or lack of same- forward revolutions of this aggressive bit would be merrily consuming aluminum at alarming rates (did I mention that the bit's "locating" spur is not at this time connected to anything but air?)
[[the template hole is 1/4". The Drill Press was utilized because the (template) casting is about 3/32 and the distance to the gasket plane is about 1/2. The hole in the gasket MUST be perfectly in line with the casting hole, but the bit rim is not long enough to remain in contact with the casting when it reaches the gasket plane (parallel to the bolt seat).

Proceeding downwards, the spur does make contact with the gasket sheet and any runout remaining is reducing, and with another few thousandths contacts the plywood back and steadies the bit. Now right about the same time or a little farther the template leaves the picture- the bit rim is only about a 1/4" and it has passed thru the wall of the template; the spur is engaging the (soft) surface of the plywood backer and the gaskmat, and the cutting resources of the bit are at- or about to be at- the gaskmat as well.
Continuing, the gaskmat is drilled through, almost. This, I think, is where the rough hole is produced running forward, by the waste being grabbed by the spinning rim/scrapers and invited along for the ride, fibers breaking before they can be cut. If I didn't say so before I should mention that a clean hole is extremely important. (I made I don't know how many test holes at varying depths to try and find the right depth for the cleanest holes. That was the part that wasn't so much fun, at the time.)

But reversing the bit's rotation and attacking the gaskmat with a less aggressive bite took care of almost all the rough cuts, and I suspect the two I had were the last, and the result of things going so swimmingly I let my guard down a bit.

So, 2 main things FOR reverse: doesn't rim-cut the (aluminum) template; much smoother- reliably- holes in gasket material. This last is critical. Each of 13 individual holes must be perfectly located, sized and smoothed. One mistake equals a new sheet of gaskmat.

Just thought of another plus-- able to clear the bit of refuse after each cut- a Must!- with a brass brush or even a finger tip, without damaging the bit, brush or finger. Little things make a job go easier.

[keakap]

My guess is that the back side of the spurs did not 'dig', but cut the gasket material anyway.

Then there is the possibility that that they were brad point or auger bits.

I use a punch if holes are small enough.

Oops, almost missed this un.

1. Your guess is a good one.

2. (No worries- the bit is indeed a Forstner.)

3. Took me a second to remember why I didn't use the punch I've used before. My "method" of precisely locating the 13 holes was to use the Part- "Cover, Oil Strainer", think "oil pan"- placed gasket-side down on the gasket sheet. The distance from the gasket surface to the top(now) is about 1/2 for most holes, to the max of about 1-3/4 (clarifying, there's about 1-21/32" of air between the gasket surface (flat) and the 'aluminum hole' furthest away).
I've never seen a punch that could do that job, at least not on this goofy stuff. Gasket material can be a pain to work with, especially in delicate designs.

Back in California I would probably hopped in the car and drove down to my local Tool Store, looked for and maybe even found a punch device of some sort.
Here? By the time I found a decent Tool Store my car would be awfully wet.

;-)

[dusty]

keakap, keep watching and I'll put up my TAC patch. I was assigned to SAC when they locked the silo doors and lowered the flag here in Tucson. It was a sad day.

I gotta study your last post a bit.