How to make an electric drill run slow?

[Clarkdale44]

Although this is indeed a hammer drill... it has a switch to turn the hammer function on and off. And obviously i am using it in hammer off mode.

Yesterday a friend came by, he told me he has the drill bit for metal. He used his titanium coated drill bit with my drill and it drilled through 5mm steel in about 5 to 7 seconds (8mm hole). We used oil and he also had this thing he called center punch with him. He used this to make a small dent in the steel where we needed to drill the hole.

The drill works fine just as long as we apply oil to cool down the metal. Also the crazy part was after the job was done, i touched his drill bit and it was barely warm. Really have i lost my senses or this titanium is bad conductor of heat?

 

[JimB]

The yellow TiN (Titanium Nitride) coating on some drills is very hard and does help to reduce wear on the material which the drill is made from.
It sounds as though the drill used by your friend was a proper HSS (High Speed Steel) drill.

When drilling holes in metal, it is good practice to mark where you want the hole using a centre punch, that stops the drill from wandering around on the surface and starting the hole where it wants, rather than where you want.

If I were drilling an 8mm diameter hole in 5mm thick steel, I would do the following:
1 Mark the position of the hole using a centre punch.
2 Drill a pilot hole, 2 or 3 mm diameter, using the centre pop as a guide.
3 Drill my 8mm hole using the pilot hole as a guide.

If the steel being drilled is tough, a small amount of oil or cutting compound to reduce the friction, is often helpful.

If you look closely at the point of a correctly sharpened twist drill, you will see that it is not a sharp point but a short line.
With larger drills this line does not cut very well and just rubs its way through the metal. That is why a small pilot hole greatly improves the cutting performance of a larger drill.

JimB

 

[Clarkdale44]

The yellow TiN (Titanium Nitride) coating on some drills is very hard and does help to reduce wear on the material which the drill is made from.
It sounds as though the drill used by your friend was a proper HSS (High Speed Steel) drill.

When drilling holes in metal, it is good practice to mark where you want the hole using a centre punch, that stops the drill from wandering around on the surface and starting the hole where it wants, rather than where you want.

If I were drilling an 8mm diameter hole in 5mm thick steel, I would do the following:
1 Mark the position of the hole using a centre punch.
2 Drill a pilot hole, 2 or 3 mm diameter, using the centre pop as a guide.
3 Drill my 8mm hole using the pilot hole as a guide.

If the steel being drilled is tough, a small amount of oil or cutting compound to reduce the friction, is often helpful.

If you look closely at the point of a correctly sharpened twist drill, you will see that it is not a sharp point but a short line.
With larger drills this line does not cut very well and just rubs its way through the metal. That is why a small pilot hole greatly improves the cutting performance of a larger drill.

JimB

Thank you... i will definitely follow these next time.

 

[KeepItSimpleStupid]

Jim did a really nice job. I just need to add something: Stainless Steels generally work harden, so it;s VERY IMPORTANT to keep it cool. It's better to take short bites and let the material cool.

Cobalt bits are harder yet. I'm slowly replacing the bits in my drill bit sets with Cobalt as they break/wear. There are drills for different materials. Speeds are generally increased for smaller holes.

Transfer punches https://www.harborfreight.com/28-piece-transfer-punch-set-3577.html are sometimes useful to mark the center of an already drilled hole. An automatic or manual center punch then makes the small dent so the bit doesn't wander. Drilling one hole and temporarily attaching the object and then transfer the other hole usually does a better job.

If using a drill press, mill or lathe you have the option of using a center drill.https://littlemachineshop.com/products/product_view.php?ProductID=1230 You can see how these will stop the bit from wandering and focus the bit in the countersunk hole. They may break without a drill press.

Sheet metal has a lot of different techniques since a regular bit drills somewhat of a triangular hole. Dishwashing soap and water makes a good lubricant for plastics. Try drilling a 5/8" hole in a 1/4" thick piece of acrylic. I ground my own tip for that.

 

[mvs sarma]

attached link helps locate special quality drill machines with variable and even reversible ones.

https://www.ebay.com/bhp/variable-speed-drill

simply lowering the voltage either by Variac or Triac, might burn the winding of the machine.

 

[mvs sarma]

Also consider the drills themselves, are they cheap carbon steel or HSS (High Speed Steel).
A 6mm carbon steel drill will not last long cutting steel at 2700rpm.
A 6mm HSS drill will get hot but will not lose its cutting edges unless you het it red hot.
As for slowing the drilling machine down, a simple phase controlled "lamp dimmer" circuit would probably work OK, provided that the thyristor/triac can handle the current.JimB

we are expected to lubricate the drilling location. I saw most workshopes doing so.
Otherwise the bit might get welded to the job under operation due to excess heat., leave alone wasting bits.

 

[KeepItSimpleStupid]

Really am i lost my senses or this titanium is bad conductor of heat?

Titanium is a very poor conductor of heat. Pure Titanium is weird. The coating is Titanium nitride. https://en.wikipedia.org/wiki/Titanium_nitride More importantly, it makes a hard coating. Aluminum is like 205 W/m-K and TiN is about 30 ish at room temp. Copper is about 380.

 

[ClydeCrashKop]

While repairing a 2 speed Makita sander years ago, I noticed that the slow speed was achieved by using a diode to only send half of the AC power to the motor.
I made a short extension cord (6 inches) with a heavy duty diode in series to slow down a grinder and it worked fine. Both were brush type motors like your drill. I don't know if that will work for other types of AC motors.

Also, cobalt drill bits are brittle. They break easily.
You need to use enough pressure. If a drill bit isn't cutting, it is rubbing. Rubbing will dull your bit & create heat. You can find a table for cutting speeds & feeds for different drill sizes and materials being drilled. I find that slower speeds and heavy feeds work best for most things.

 

[PatM]

Maybe a variac?

AC motors speed is controlled by the line frequency not the voltage.
A variac would only vary the voltage and not work to control the speed.

 

[kubeek]

AC motors speed is controlled by the line frequency not the voltage.
A variac would only vary the voltage and not work to control the speed.

If the motor is the usual commutator type then frequency should not matter and the voltage will have a big effect on the speed.

 

[shortbus=]

As another note to drill bits, many of the "made in China" bits are not ground/sharpened correctly. One of my sons bought a complete set, number, letter and fractional sizes. Most of them wouldn't cut in metal, there was no clearance angle ground on the cutting end. Without a clearance on the tip, the whole cutting edge rubs instead of cutting. After sharpening them for him, they worked fine. https://www.google.com/search?q=dri...=Y2YqV6ioO4GAmgGbraXoCA#imgrc=Z0WsOBH_de-ubM: