Pilllar drill speed reduction

I have an approx 15 year old Axminster medium-sized pillar drill. It has the usual pulley arrangement, which I've configured for the slowest speed. However, when drilling holes >10mm in mild steel (6mm) it stalls. I think my drill bits are sharp and I'm using cutting oil. Am I asking too much of this machine? Would it benefit from a speed reducer like this?

https://www.youtube.com/watch?v=PsBs064cyOI

When you say stall, is it just the spindle that stops or the motor too? If the latter the motor would probably make a loud hum and get hot. If it's just the spindle then maybe the belt tension needs increasing or you need a new belt. I wouldn't expect a medium sized pillar drill to have a problem with a 10mm hole in ms. I use to have one of the little pillar drills and I think I used to drill half inch holes in steel without a problem if I took it slow.

I agree with John generally except to say that I can stall my mill-drill on a 6mm drill if I don't clear the swarf often enough. Especially if I go straight in with the 6mm and not drill a pilot first. Cutting oil tends to increase that problem in my experience.

(these problems are 3 kinds of 'ell aren't they ..... sorry - couldn't resist )

I must be one of the lucky ones ! I have a 20+ year old pillar drill 16 speed,with which I can drill 12mm holes,no problem,using a speed of around 500 rpm,sometimes higher,if I,m too lazy to change the speed.

I also have a cheapy,cheapy bench drill from Aldi,5 speed,I think,which has no bother drilling 1/2" holes.,so I suspect that your belt is slipping,or just needs to be replaced.

Now that I think of it,the belts on my 20 y/o have never been replaced. This machine can also handle 1" drills without slipping,so I would say check your belt first .

And it always helps to drill a small 'pilot' hole first, with anything over 10mm. Just slightly larger than the 'solid' centre of the big drill.

Tim

Have a look at the motor rating plate and see what power rating it has. It's surprising how many power tools are equipped with a motor that's nowhere near big enough for the job

Wot's changed? Did it used to motor through, or has it always been reluctant and (in old age) just got more so?

A medium sized drill to me is 3/8 or 1/2 inch capacity, and most "budget" drills will just about do this though they tend to be a bit high geared. Slowing them down by gearing or belt sizes is always going to help, but don't get side-tracked into variable speed if the machine is already on the limit of the motor rating. If you do gear it down will it still be a happy bunny drilling very small holes?

Hopefully the drill has a nameplate on it giving speeds and capacities - if it is rated to drill a 10 or 12 mm hole but has decided not to then I'd look at the drive belts first, as John Haine suggests above, if that looks OK then I fear the motor is poorly. Various things can go wrong with a motor as anno domini's accumulate, but most will give obvious signs of distress by way of hot bits which should run cool, horrible buzzy noises from the motor etc. Single phase or three phase, if it is single is it capacitor run (two capacitors) and if so there's a suspicion that the run capacitor or winding is faulty etc etc. Neil has done a very lucid sketch on another thread in the last day or so explaining the intricacies of a single phase motor with a draggy centrifugal switch.

Check the drive belt isn't stiff with old age (don't I sympathise!) or even beginning to de-laminate. Also bear in mind a lot of these drills used undersized drive pulleys to keep the size of the machine compact. The drive belts don't last for ever going round these little pulleys, especially pulling a large drill at or above the max torque capability of the machine. Experience suggests many of them run a bit fast for the max size of drill specified. A new good quality drive belt can absolutely transform the capabilities of a drilling machine. Are the pulleys alloy, if so have they got a wear groove in the wall of the vee which has altered the drive vee angle? Is the bottom of the drive vee polished, 'cos if so the belt is bearing on the bottom of the vee not on the sides at all.

The other thing that can affect the way it drills is how greedy the drill is, by which I mean how it has been sharpened. A drill with a lot of clearance will grab and be difficult to keep turning, whereas one which is a bit less eager will behave in a more civilized fashion and need less torque to achieve steady progress. Comments earlier about drilling a pilot hole - I use a "rule of two or three" pyramid - so drill a 4 mm pilot for a 12 mm drill, anything over 5 mm needs a pilot hole first. Too big a pilot hole can lead to its own problems, as the drill tends to grab unless it's having to work for its cutting. You can stone a bit of the rake angle off the lip of the drill to calm it down, but you really shouldn't need to unless you're cutting something grabby like green brass or cast iron.

If you can give us more details of the model or construction of the machine we can probably muse further, for example is it pulley and drive belt drive, vee belt or poly-vee, is a variable speed control fitted and if so what speed range do you use, is the motor an induction motor or a brush type. The OP says it is a middle range Axminster Tools machine so we probably guess it's a 1400 rpm induction motor rated at about 1/2 - 2/3 HP, pulley drive with plain vee belts, no variable speed. But confirmation would help. also what speeds are indicated for the different pulley combinations

A variation on a theme, I once had a torque problem on my old Clarke bench drill. As it turned out, it wasn't the belt that was slipping, but the driven pulley on top of the quill / spindle. The grub screw holding the pulley to the shaft had come loose.

Be a sport and treat the old girl to a new belt or belts. (Not sure from your description which it is.) Rubber does not last forever. And if they have been run loose and allowed to slip belts will almost certainly be glazed and slippery.

I had another go at this last night. The drill is a 0.375KW 1420rpm plain pulley drive with V belts. The pulleys are plastic and the belts look to be in good condition. I have set the pulleys to be on the slowest speed of 280rpm.

I tried drilling some 5mm MS with a 10mm bit, no pilot hole. I did get through eventually but the whole machine would stall if I pressed too hard. No belt slippage or strange noises, everything just stopped. I also tried it with a 12mm bit which went a bit better (sharper drill I assume). I suppose I've reached the limits of this machine?

I do have a spare 1HP induction motor I could transplant into it, but it is 2800rpm, so the speeds would be a bit off. I also have a 3HP DC motor from a treadmill that I could use, but I hear that these kind of motors don't produce much torque at low rpm, which is why I was interested in the pull gear mentioned in my first post.

If you're not going to use pilot holes then use a decent quality 4-facet ground drill for lower cutting forces.

Andrew

When drilling a hole of this size I would normally drill a pilot hole first, but this was just an experiment to see what my machine is capable of. The speed is probably a bit too slow as well as I'd set it to the slowest as I'd previously been using a hole saw and forgot to change it back.

'I also tried it with a 12mm bit which went a bit better (sharper drill I assume)'

You're probably right, and perhaps your twist drills are the problem? True the machine is on the low power side, but it shouldn't be struggling with 10mm in mild steel.

In these situations trust nothing!

• Are you certain the work piece really is mild steel? ( Beware of random scrap metal. Other steels can be very hard, or can work-harden. Not nice. )
• Are you certain your drills are suitable? (DIY store drills may be carbon steel, fine for woodwork, but easily blunted when used on metal. HSS drills should be better, but cheap HSS may not be. TiN coated drills are sometimes sheep in wolves clothing. Better to buy drills intended for metal, and - if you're into serious drilling - be prepared to pay serious money for them! )
• Are you certain your drills are sharp, and that the tip is properly ground? (Even new drills are sometimes faulty)
• Is it possible you ruined the drill? Two ways of doing it. 1) Overheat & stress the drill by cutting too deeply, or; 2) Blunt the drill by destroying the sharp edge by rubbing it on the work. I think this is a common beginner mistake and it's more likely on a light drill press with a small motor. Don't pussyfoot!
• The machine may require attention (wrong pulley ratio, slipping belt, slipping chuck)
• The motor may be faulty.

If a 12mm drill is doing better than a 10mm, I think bad twist drills are a strong candidate. Might be they were unsuitable to start with, or that you're drilling holes in something vile, or that poor technique blunted the drill. Once a drill loses it's edge, it gradually converts itself into a brake. On a big machine, the symptom might be heat, a small one might just stall.

Where did you get the drills? Any chance of posting a close-up photo of the tips?

Dave