[Argofanatic]

Hi, a bit of silly question but I'm curious to find out what you guys would do.

I have to drill a whackload (technical jargon for a whole bunch) of 5/16 holes in 1/4 aluminum plate (corner gussets) during my router build. I have a mill drill and I'm wondering if I'm better off using an end mill or a twist drill.

Thanks,
Marc.

[DareBee]

Drills are for drilling and mills are for milling.
They both can be used for the other but they are not designed for it.
There are exceptions to every rule though.

[lgreeves]

TiAlN coated Screw Machine length solid carbide drill. Make holes fast and lots of them.

[larry53]

Hi, a bit of silly question but I'm curious to find out what you guys would do.

I have to drill a whackload (technical jargon for a whole bunch) of 5/16 holes in 1/4 aluminum plate (corner gussets) during my router build. I have a mill drill and I'm wondering if I'm better off using an end mill or a twist drill.

Thanks,
Marc.

I would use a center cut endmill if I was plunging a blind hole that required a flat bottom. I would use a drill bit if it is a through hole.

[Argofanatic]

Thanks for the replies.

Through holes with a twist drill it is!

[Willbird]

Just one note, endmills to not make flat bottoms, :-).

Just for fun take an endmill, and a flat surface, your mill table maybe, now place a clean piece of paper on the table, the table is never clean and that is good for THIS, now press ene endmill gently against the paper, and rotate it backwards about 1/4 turn, and lift it up. Now look at the reverse side of the paper, you will see that the endmill has a dish. I learned this trick when I was taught how to sharpen endmills, the tool sharp guys call that a "walking cutter" and it lets the tool cut across a surface instead of trying to rotate about a high center. You CAN have them sharpened as true flat bottom, the amount of dish is not a lot but it IS there.

Now about drilling holes, if you ever get some NASTY stuff to try to get a hole in you will find that if you can get ANY kind of pilot drill thru first that an endmill will then make a hole in stuff a drill won't touch..

it is common to "bore" holes to location with an endmill, to do this really nicely you need to reduce the body of the endmill flutes so only the last 1/2" dia is still to full size, this stops the cutting pressure from "wedging" the tool over as you move it through the part, works pretty slick, and it is a nice use for re-sharpened endmills because you can say drill .437, "bore" to .490 with a re-sharp endmill relieved like I mentioned, then ream for size, and get nice size, and near perfect location every time :-).

Bill

[mrk]

As a related question, how do you calculate feed rate for the down movement for end mills vs. drills? I assume you can't just go the same speed for down movement as you do for X/Y and I assume drills and end mills need different speeds.

[Cory]

As a related question, how do you calculate feed rate for the down movement for end mills vs. drills? I assume you can't just go the same speed for down movement as you do for X/Y and I assume drills and end mills need different speeds.

I was taught 1/2 the feed of normal milling when plunging.

[Willbird]

It all depends :-) If I were milling a slot .250 long and .125 wide .125 deep I would use a 3/32 solid carbide 4 flute center cutting endmill (on steel part) I would run it 6451 rpm(150 sfm), and I would plunge down .001" per rev feed, when I hit bottom I would profile the slot at .005" per rev feed. This is quite conservative but it will work in A2, D2, 8620, 4140HT, and 6150...doing it that way saves several toolchanges required to spot drill and pre drill...I used this method often in 5 axis work when this type of slot (for a dowel pin) was the only work done at that end of the part, on fadal 5 axis machine it is common to have to move X and Y to get room for a toolchange so avoiding one is a blessing :-). Fadals are also not super rigid thus the lower than wide open throttle sfm. You can run more with smaller cutters but get up near 1/2" and they start to chaterrrrrrrrrrr :-)....for short runs it is cheaper to NOT break a cutter and ruin the part IMHO :-).

S0 I guess my short answer for steel is start at .001" per rev and work up if you only have ONE endmill to do the job with :-)...this is plunging right into solid metal, and not often the BEST solution, but sometimes it fits the job to a T.

Bill

[justCNCit]

It all depends :-) If I were milling a slot .250 long and .125 wide .125 deep I would use a 3/32 solid carbide 4 flute center cutting endmill (on steel part) I would run it 6451 rpm(150 sfm), and I would plunge down .001" per rev feed, when I hit bottom I would profile the slot at .005" per rev feed. This is quite conservative but it will work in A2, D2, 8620, 4140HT, and 6150...doing it that way saves several toolchanges required to spot drill and pre drill...I used this method often in 5 axis work when this type of slot (for a dowel pin) was the only work done at that end of the part, on fadal 5 axis machine it is common to have to move X and Y to get room for a toolchange so avoiding one is a blessing :-). Fadals are also not super rigid thus the lower than wide open throttle sfm. You can run more with smaller cutters but get up near 1/2" and they start to chaterrrrrrrrrrr :-)....for short runs it is cheaper to NOT break a cutter and ruin the part IMHO :-).

S0 I guess my short answer for steel is start at .001" per rev and work up if you only have ONE endmill to do the job with :-)...this is plunging right into solid metal, and not often the BEST solution, but sometimes it fits the job to a T.

Bill

If you are talking about milling a slot, why do you mention ever having to use a spot drill and pre drill? am I missing something here?

[Willbird]

Typically in the shops I have worked in it was normal practice to drill a hole first...whether the slot is blind or thru to the other side..often it was with a tool that was also used on other features, These slots as I said were only 2 dia long, so there was really not enough room to get a good ramp cut down to the bottom, and our programs were made with calculator and pencil and paper, not CAM :-). So running a pilot hole down to the bottom of the slot first means you only have to plunge the endmill the amount of the drill tip, which is less prone to break a cutter.

Bill

[dertsap]

if you drill with a good stubby , a typical hss will drill accurately and fast in aluminum plate

[Willbird]

Yes for many things a screw machine drill running true does a nice job without any spot drill first :-)

Bill

[Zumba]

A screw machine drill is good but a 135º split point screw machine drill is even better.

[larry53]

A screw machine drill is good but a 135º split point screw machine drill is even better.

Can this drill bit be used to start the hole,without center drilling first?

[Pres]

Yes, if the top surface is flat and smooth a split point works good.
(it should be against the law to sell drill bits that are NOT split point)

Another option I used alot was a short 2 flute carbide end mill sharpened to 135d split point.
I could use it for milling od & id, drill holes & make holes that were larger by using G02/G03.
That saved alot of tool changes on my "manual tool changer" mill.
YMMV,
Pres