Drill press conversion

[James Boster]

I get tired of changing belts to change speed all the time. I have a 3/4 hp DC motor and controller that I'm planning on putting on the drill press. I never see one that is electronically variable speed. Is there a reason this won't work. I recently aquired a walker turner RAM drill:D :D with 16 speeds but I would like to put this DC motor on it to make it easier to change speed. Any input? Thanks

[Rick Lizek]

It's a common practice nowadays, especially on lathes and such. More often done with three phase motors and VFDs and typically a step pulley is still used to keep the torque on lower rpms.

[Steve Stube]

If your Ram Drill Press is already equipped with a 3 phase motor then adding a variable frequency drive will certainly give you the variable speed you are seeking. Fractional HP VFD's can be obtained for probably less than a hundred at that "on-line" auction house.

If it is single phase now - then "a" DC motor and control might be a smoother way to go and less of a learning curve IMHO compared to the VFD. The "a" is my fudge factor as I have no idea what motor and controller you may have and not all DC motors and DC motor controllers are equal. If you already have a good DC motor/controller combination - GREAT. As already cautioned you probably will want to leave yourself some speed change capability (pulley/belt changes) for low end torque. The only problem you might have is fitting (physically) a DC motor in the rather crowded space allowed on that drill press between the ram and hinged belt change cover guard. my .02 cents

[Jim Becker]

I could be wrong, but I believe that the DC motor may have torque deficiencies at very low speeds...perhaps someone with motor knowledge can confirm/deny that.

[Don Baer]

Jim is correct.

OK here my 2 cents worth based on my 30 years of applying various DC and AC variable speed systems.

A general purpose DC motor is a constant torque device that means that the torque is the same at 87 RPM as it ius at 1750 RPMs. When drilling smaller bits can run at higher speeds and require lower torque. Larger bits usualy are run at lower speeds and require higher torque. The motor must be selected for the highest torque required (The larger bits) and the max speed should be based on the smallist bits. A 1750 RPM 3/4 HP DC Motor will products 27 inch.lbs of torque.

Someone suggested a VFD (Variable frequency drive) They also are a constant torque device when run from 0-base speed (1750 RPM's for a 4 pole motor) but some have the ability to run above base speed in a constant frequency mode. Then they are a constant HP device. The toque decreases as the speed increases. They are more sutible for a drill press or a lathe.

That said if you can do trade off with a DC Motor by selecting a bigger motor so that you have enough toque for the larger bits and enough speed for the smaller bits I..e using a 3/4 HP motor to replace a 1/4 HP constant speed motor.

Remember when you change the speed with a pulley system the when you slow down the speed the pulley acts as a torque multiplier.

If someone wants the theory behind this I would be glad to provide it but I think for this forum it would be TMI.

[Dev Emch]

Wow Don, you covered almost everything to be said.:D One question however. What does TMI stand for?

But it all boils down to torque. The newer oliver patternmaker lathes that replaced the 20 series often had a massive DC motor with a huge DC controller. When getting into the lower speeds, you could tell the motor was having issues and that the controller was sounding like a transformer supplying juice to the delorean on back to the future. That is why I still prefer the older three phase motor with the lima drive transmission and step pulleys. You could spin a 20-C so slow that you can watch the dot going around and around. But try to stop this this shaft! You cannt!

I was working with the idea of using a VFD to boost the speed of my porter jointer as its a DMD forced to run at 3450 RPM. I can get it to run at 6500 RPM but the lose of toque is significant and the 20 inch cutter head needs that torque when it bites into a deep cut. Once again, its about torque. If I were running a tiny router bit, no worries. But a 20 inch cutter head that weighs 50 or 60 pounds is a problem.

[Steve Stube]

Lets see, there are permanent magnetic DC motors and there are wound DC motors. The later category includes, Series Wound, Shunt Wound and Compound Wound plus some specials. They do not behave the same, there torque curves are different. Then there are a multitude of DC controller types, Half Wave, Full Wave, SCR's, PWM and variations of these.

Some DC motor/controller combinations won't be worth a squat for the drill press application and some will provide all the power you want plus variable speed. One needs to match the motor to the controller and both of these to the application.

BTW, I have no idea what a general purpose DC motor is but would like to learn. I do agree with Don that to go any further might be TMI (too much information) for this forum.

I scratch built DC motor controllers primarily for Shunt and Compound wound DC motors over the past 33 years to provided variable speed and plug reversing (where beneficial) on metal and wood working machinery. Initially for my own shop machines, then on machines I reconditioned for sale and eventually for some grateful others that helped with my hobby shop expansion activities. Rotary phase converters followed a similar progression but with far fewer units built. I had fun at it.

[James Boster]

The motor and conroller I have are a Woods ultracon scr controller and a matching Woods 3/4 hp motor, both new. the controller has a dial for variable speed and one for torque setting. I may rethink this venture but if I get time I will probably try it, if It don't work I'm not out anything but time. which we all have so much of these days.:D

[Steve Stube]

James, by all means give it a try (I hope I didn't sound negative to the idea) and I for one would be interested to hear the results. Woods offers some fine equipment in VFD's but I'm not familiar with their DC controllers. The fact that the motor/controller is already matched up is a real headstart. Is it a PM motor? 3/4 HP is a good size to be working with. I sure hope you can find the time to experiment with this modification.

On another note, if you have any stickness in the Ram travel there is a guy selling bearings on eBay that are a match to my Rockwell (and probably yours too). Set of ten for maybe $12.00 total including S&H (only 8 required for a complete change-out). I picked up a spare set figuring if I had to buy one bearing from Delta for it, it would probably be much more than $12.00. I have a Thompson Mill/Drill (x-y tracer) table I hope to use on the Ram drill press to mill wooden patterns and signage - it's on the list.

[James Boster]

Steve, I did not take your input as negative. My drill doesn't need bearings but I too would be interested in picking up a spare set if you could pm the contact info for this guy. Thanks.

[Steve Stube]

You have it in your box.