Sharpened large drillbits not cutting

[-Matt-]

Agree with all said. Where I work we have a big gear head 4 bank pillar drill and its slowest speed is 104rpm. Might still be a little quick in some ways but I've put an inch drill through 15mm plate no problems. Bit softer on pressure and a good feed of cutting grease, from pilot to finished in about 10 minutes.
I'm also interested in your sharpening, I assume you've the angles all right?

 

[Ttrees]

Ya, have even experimented with various angles and went back to the regular shape ...
Somewhere between 118 and 120 I believe.
Easiest way to see, is by getting two large nuts and putting them together to reference the tip against .
Using a disc sander, so a bit mire straight forward ...although not thinning the web....
Doesn't seem much point, as I am using the outer part of the drills for enlarging large pilot holes at 2mm stages.
Making sure to measure the cutting edges so they are the same length.
Started out grinding with the drill aimed to the left, but switched after that to the opposite orientation as I find it
smoother to get a swooping single facet

Have found these videos good watching ... in order of appearance.
https://www.youtube.com/watch?v=xJtYBU2BAMY

https://www.youtube.com/watch?v=FgcESWoJ3CU

https://www.youtube.com/watch?v=y0SQkzScQk0

Tom

 

[-Matt-]

Thats how I was taught using the two nuts.
Can do it by eye now so it must work I guess!

 

[novocaine]

so you talk about your included angle, what are you grinding the relief too?
for very hard stuff you want an included angle i the 125-135 region, especially on big stuff like that, although as you are step drilling it, the angle makes very little difference.
can you take a few pictures of the tip of the drill bit, preferable straight on so we can see the angles a bit better.

have fun, and do as everybody says above, go slow. if you can't go slow, lubricate.

 

[Ttrees]

I will take a piccy or two of the bits later on tonight,
I have been getting good at grinding the relief as I mentioned that I switched orientation after a while.
I done this because I found I can get a nice swooping single facet easier, with the drill aiming towards the right and lifting up to
taper the heel as to not ride on the heel .
This was what I thought the problem could be at a stage.
I wonder how long I can remember this skill and sharpen a bit first time...say after a break..
I really felt I got it down now though
Not that I'm going to be taking a break from drilling anytime soon (hammer)
Have to measure that shaft today
Tom

 

[Ttrees]

Checked the motor shaft today and the shaft isint as small as I thought it was...
Defiantly not 15/16", so I am quite happy as I don't have to spend 50 odd quid on imperial bits .
If the shaft proves to small in spots it will get a bead of weld ....
So I just drilled the sleeve out to 24mm and it was easy and quick...
I had to sharpen it beforehand and take a lot off the heel for there to be an acceptable relief angle.

The metal piece was not hardened or hot or neither was the bit
Guessing this bit was not used as often ..I can't remember
So I am baffled as to why this drill was so quick .

I still suspect the others have a worn taper in them ?
The only thing I can think of is I ground more relief on this one and didn't do it in one facet as it would have been wasteful.
,it was a mess before I started (angle wise)
I still think the relief on the other bits is more than enough though.

Now to make a jig that will score a line for the outside of the sleeve so I can grind and file to it.

This subject should be well discussed
I can't be the only one using large cheap bits with a regular pillar drill .

Thoughts ?

 

[Ttrees]

Hi again folks
Doesn't seem like there is folks who use cheap large bits in a pillar drill ...
Strange as I got my old drill for 40 pounds plus the petrol to get there, and the bits cost about 25 say ...
This kinda thing should not be uncommon.
I must point out that it is not necessary to have a real slow drill here with a half ton power feed unit.
You can drill slower than the drill RPM if you want to, by not allowing it to speed up again and feeding it into the work.
So on to measure how tightly this sleeve fits on the shaft ....
Fingers crossed its a good fit .
then its a case of grinding a down to the line, and then filing down to get a press fit.
I mentioned that the pulley is aluminum so I should be able to mark it with the sleeve and file/sand/scrape the high spots to
get a nice press fit .
The jig I made for marking is not precise enough to trust.
Made another score on the pulley, as I only scored the line to the edge of the out of center edge last time.
this one will make it perfectly centered .
I might wrap a bar around paper and sand it down to final dimensions .
Goin at the base for the saw today though, so I can clean the shop up a bit.
Will keep you updated
Tom

 

[Ttrees]

Got back workin on the sleeve today after painting the mobile base I was making.
Nearly getting close ....Never filed on a turning piece before, quite fun
especially after angle grinding for the last few days.
Will be getting close tomorrow and making the sleeve fit on the pulley,
After that making a new key.

I think I might have to take this sleeve off to file the key slot ...that won't be easy.

Close to getting this tablesaw going
Wish me luck
Tom

 

[AndyT]

I think the reason why there weren't lots of responses from other people drilling big holes is possibly that many hobby metalworkers will have a lathe and use that instead, to bore big holes rather than drill them. A boring bar covers a wide range of hole sizes and costs a lot less than a set of large bits. Also, you don't need so much power as you can take a very fine shaving.

I must say it's interesting to see someone problem solving to suit the tools available but I wonder if you have thought about getting a lathe - you might enjoy the extra scope it would give you for making bespoke parts.

 

[DTR]

I think the reason why there weren't lots of responses from other people drilling big holes is possibly that many hobby metalworkers will have a lathe and use that instead, to bore big holes rather than drill them. A boring bar covers a wide range of hole sizes and costs a lot less than a set of large bits. Also, you don't need so much power as you can take a very fine shaving.

Absolutely this. Despite having a vintage Walker Turner pillar drill and a jig borer(!), I still resort to the lathe for most things over 3/8" diameter. Boring has other advantage too, such as more accurately sized and shaped bores, better surface finish, and no wandering off course.

Edit: Just to clarify, I do use bigger drill bits in the lathe up to about 3/4". The lathe is quite comfortable with these due to the slow speed and high torque. My Walker Turner pillar drill has the option of an intermediate (third) pulley to gear the spindle down further; this is something I want to do one day.

 

[Ttrees]

I have thought about getting a metal lathe Andy, but there's a few more tools to acquire first before going down that rabbet hole.
A Thicknesser planer might be handy... although, I am really set on making a large cyclone DC after working on this saw....
And the other one.
I nearly bought a wood lathe not so long ago. that's on the list too

But you're right a metal lathe would open up a world of possibility's, never needing to buy anything again.
Other than tooling and everything else that you might "need" for it :roll:

I'm always looking around, for an old lump needing work that can be fixed up, that's only weighing a moderate amount.
I have plenty of stuff to do in the meantime though.
Hopefully get this done today or tomorrow.
Tom

 

[heimlaga]

I occasionally drill holes up to 31 mm in diametre in my Arboga G2508 drill press. At 100 RPM for anything over 15 or 16 mm in diametre. With lots of coolant.
The biggest hole I have ever drilled was 30 mm in diametre and some 60 mm deep when I drilled out the shaft from a flat belt pulley. I think I was seriously pushing the limits of my drillpress doing that.

Though a 20 mm hole is very big for any ordinary belt driven drill press.

The main downside with drilling out a hole in a pulley is that drilled holes usually aren't round. Particularly not if there is a key slot or a hole for a grub screw somewhere. Making the hole centered would be very hard too.
I always aske a machinist friend to bore out pulles for me in his lathe.