[QuinnSjoblom]

So what I need to do is extend a couple small carbide drills by a couple inches. I need a 2.1mm drill and 2.5mm that needs to reach in 1 1/2 inches with no more than 1/4 inch shaft. Actual drilling depth is only about 10mm. Easiest would be to just find carbide drills with a long 1/4 shank, but can't find any. What I picture is just a 1/4 shaft with a 1/8 bore at one end, maybe 1/2 inch deep and some set screws to lock in 1/8 shank tooling. Does such a thing exist or will I just need to make my own? Any other options?

[CitizenOfDreams]

Here are some extra long carbide drills on eBay:
https://www.ebay.com/itm/KLOT-10pcs-...WAg:rk:80:pf:0

They have straight shanks, so you will need appropriately sized collets.

[QuinnSjoblom]

Here are some extra long carbide drills on eBay:
https://www.ebay.com/itm/KLOT-10pcs-...WAg:rk:80:pf:0



They have straight shanks, so you will need appropriately sized collets.

Oh wow, those are long. Ok, that's one option. Although I would prefer to keep some rigidity with a larger shank since I'm only drilling 10mm deep. Also would be nice to stick with 1/4 collet since most of my other tools are 1/4. With these I'm sure spotting is gonna be required. I feel like a short carbide drill on 2 inches of 1/4 shank would give pretty good locational accuracy without spotting.

Another thing is, I may end up rigid tapping these holes so the tap would also need extended that far.
I think there's a way I could make these extensions myself. I don't have a lathe, but I could start by drilling/reaming a 1/8 hole into a peice of material, secure a 1/8 drill, then reamer into that hole, chuck my 1/4 extension material into the spindle, drill/ream the hole into the end of it with the stationary tool in the previously drilled hole. Although it would be nice if the extensions were carbide and I'm sure I won't be drilling that

[deadlykitten]

hi, isn't there a custom tools shop arround you ? just asking ... kindly

[hanermo]

You want to drill about 10 mm deep, with 2.1 mm drill, extended about 30 mm.
The D/L is 5:1 at 2.1/10 mm, and 30 mm out it is 15:1.

This is extremely challenging aka near impossible (in steel) with carbide drills.

Carbide is brittle and any spindle TIR errors over 0.01 - 0.02 mm at 37 mm out from the spindle will probably shatter the drill bit.

Because You probably don´t have a uber good industrial spindle, heat shrink collets etc. allowing sub 0.01 mm TIR 37 mm out.
And around 3-5-7000 rpm spindle speeds for 2.1 mm.

The extensions could easily be made in a lathe, even loose shafting and industrial type epoxy would work.
Can you make a jig to maintain a straight drill 37 mm out coincident with the extension shaft, while the epoxy sets ?

HSS / co drills would probably work fine, they are flexible.

Everything depends.
How many holes, how fast, what material, how straight, what spindle and machine, etc.

Simple HSS/co drills will easily drill 10 mm into steel at 37 mm out on a basic poor import drill press.

But the hole will not be straight, or on size.
Wandering hole, banana shaped, lobed, etc.
Double reaming can get the hole pretty straight and very much on-size.

A boring head on a mill can easily make a straight on-size hole of 2.1 mm at 37 mm out.
It needs special boring bars.

[QuinnSjoblom]

You want to drill about 10 mm deep, with 2.1 mm drill, extended about 30 mm.
The D/L is 5:1 at 2.1/10 mm, and 30 mm out it is 15:1.

This is extremely challenging aka near impossible (in steel) with carbide drills.

Carbide is brittle and any spindle TIR errors over 0.01 - 0.02 mm at 37 mm out from the spindle will probably shatter the drill bit.

Because You probably don´t have a uber good industrial spindle, heat shrink collets etc. allowing sub 0.01 mm TIR 37 mm out.
And around 3-5-7000 rpm spindle speeds for 2.1 mm.

The extensions could easily be made in a lathe, even loose shafting and industrial type epoxy would work.
Can you make a jig to maintain a straight drill 37 mm out coincident with the extension shaft, while the epoxy sets ?

HSS / co drills would probably work fine, they are flexible.

Everything depends.
How many holes, how fast, what material, how straight, what spindle and machine, etc.

Simple HSS/co drills will easily drill 10 mm into steel at 37 mm out on a basic poor import drill press.

But the hole will not be straight, or on size.
Wandering hole, banana shaped, lobed, etc.
Double reaming can get the hole pretty straight and very much on-size.

A boring head on a mill can easily make a straight on-size hole of 2.1 mm at 37 mm out.
It needs special boring bars.

Ok, I'll take all that into consideration. Luckily it's just aluminum. I've never ran a drill this far out, but with a reduced shank 1/4 endmill at 70mm out, I get about a thou of runout, so I think I can be within .02mm at 37mm out. I can also think about better ways to reduce this length. What I'm actually doing is building a 4 inch square by 12in ling horizontal tombstone, driven by 4th axis at on end, bearing support at other end. I want to do small scale production on some aluminum parts that need drilled on the edges. Doing it on the tombstone will give access to the side edges of parts for drilling, but some of them are much narrower than the tombstone and this is why I need to reach in so far. I'll start modeling some things up and see what I can do. I could maybe space those parts up off the tombstone far enough for the er nut to clear, then I won't need to extend drills

[deadlykitten]

hello again, check the hss drills

i have a new one in my hand : o2.1 active_length=23.5 total_length=49

such dimensions are common, and it may suit your setup / kindly