Build Log – Homemade Rotary tool

Update -: After approx 20 hours of cumulative use, this tool collapsed under it’s own power and weight. The Brushless motor and misalignment caused vibrations so strong that the MDF bearing enclosure crumbled. An Aluminum housing for bearing is must and the Motor should be normal brushed type and not brushless one for handheld tool use.

Building some tools for your project work is fun. Sometimes it is economical too because it saves you from spending on something which will be rarely used. I already have two electric drills with a drill press stand but don’t have a rotary tool. One cannot simply drill PCBs with big drills. I had a simple drill press type motor and chuck arrangement made by my father for drilling PCBs in past, which crashed after more than 7 years of usage. Some benefits of rotary tools is they create less noise, are lightweight and there are loads of attachments available in market for variety of tasks.

So i decided to build one with reasonable power and capable of holding bits from 0.5mm to 4mm. After going through the inventory of available options, my range was restricted to 0.5mm to 3.2mm bits. Following is a basic 2D design i have created in Google Sketchup. With my limited knowledge of machining i give myself a liberty of having a big margin of error :-).

 

Rotary_tool_diagram

 

I know it is blurred. Click on above image to see it clearly ;-) . The Diagram is self explanatory.

My next articles will show further development in creation of “Homemade Rotary Tool”….

Creating a homemade rotary tool consuming at least 60watts of power and delivering most of it mechanically was my goal initially. Hence there was no option other than using a brushless motor due to the efficiency it delivers. In fact this whole project started because i had an outrunner brushless motor CF2822 lying around. I bought a 20Amp ESC for it to work on 15Volts, consume and convert 300Watts in theory. Well that’s not possible. with 15 volts supply the max RPM can be 18000.

 

Homemade Rotary tool - DIY
Homemade Rotary tool – DIY – Brushless motor and 20A ESC

 

I have also created a 5mm dia. extension to existing 3.2mm shaft of brushless motor (you will know why) and covered it with another sleeve as the total diameter needed was 7mm. The base where the motor is fitted is 36mm in Diameter and made of MDF. Next hurdle was getting a good shaft with a collet holding capabilities. There were couple of Pin vises i had bought from Local market. They are available In india for 40INR (0.72USD approx) a piece. The external Diameter of the Pin vise is 7.5mm and it was impossible to find a bearing with this ID in local market. Finally i settled with a 7mm ID bearings with a big question of what to do with Pin Vise.

 

Homemade Rotary tool - DIY
Pin vise, Bearings and collet

 

I did cut the Pin vise to cut off one of the end. After fitting a 7mm bearing in drill press vise, fitting one end barely in bearing and other in drill’s chuck, i was able to grind the pin vise. Using a file i machined the Pin vise to make it’s outer diameter close to 7mm. See this video to get an idea about this.

 

Homemade Rotary tool - DIY
Homemade Rotary tool – DIY – Machined Pin Vise
Homemade Rotary tool - DIY
Homemade Rotary tool – DIY – Pin vise machined

 

See the irregular thickness of wall of this pin vise, which forced me to use the outer side of wall for rotating it. I also fitted one brass nut i had in junk. It fits perfectly to the vise. I soldered it to the shaft. Next i prepared a round MDF holder for bearings. I used a hole saw to take out a piece of 40mm and then further reduced it’s diameter to 36mm so that it can fit into the 40mm PVC pipe. This PVC pipe has wall thickness of 2mm.

 

Homemade Rotary tool - DIY
MDF bearing holder

 

Diameter of inner hole is slightly less than 22mm, to fit the Bearings with 22mm OD. With a ring (made using a common 1mm dia. wire) to make a gap between bearings, i fitted the bearings along with the shaft. Unfortuanately one of the bearing was slightly loose, hence i had to apply a superglue.

 

Homemade Rotary tool - DIY
Homemade Rotary tool – DIY – Pin Vise converted and fitted with Bearings

 

Sorry i accidentally deleted the front photo. But the front side will be visible in next Article of my Homemade rotary tool.

Once the bearing and collet assembly was in place, it was time to couple it to the motor. Since i am using a some unsuitable materials like MDF and PVC for this purpose, some or the other alignment issues were bound to happen. I tried making almost 7-8 couplings using a 12mm dia. aluminium rod without any success. It was always off-center and putting unnecessary pressure on Motor as well as it’s small bearings.

Then i switched to flexible coupling. I used a small plastic pipe with fairly thick walls. Glued it to the Pin vise and increased the shaft diameter of motor using another homemade extension( as described in previous post) to match the coupling. Below you can see the flex coupling.

Homemade Rotary tool - DIY

Homemade Rotary tool – DIY – Motor, Coupler and Collet holder

 

Following image shows the coupled motor shaft and pin vise.

 

Homemade Rotary tool - DIY

Homemade Rotary tool – DIY – Coupled motor and shaft

 

It looks like following after putting everything in the PVC pipe and fixed using screws.

 

Homemade Rotary tool - DIY

Homemade Rotary tool – DIY Almost Completed

 

One more view…

Homemade Rotary tool - DIY

Homemade Rotary tool – DIY – Almost Completed

 

Next comes a speed control. I am already started using this tool for drilling the PCBs and believe me, this tool is a overkill for PCB drilling. For speed control i have prepared a small circuit of servo controller using NE555. There is a pile of information available on internet about this circuit. I will post the schematic  and a youtube video soon. Although currently the speed is fixed and i’m using a switch to start/ stop the motor, my intention is to use a variable resistor for better speed control.

Homemade Rotary tool - DIY

Homemade Rotary tool – DIY – Servo controller circuit

 

Apart from all the usefulness, I observed some Issues as well,

  • The bearings need some robust housing around them. MDF is not a right material. I feel it should be aluminium. There might be minute wobbling of bearing which leads to overheating.
  • The bearings should be high RPM type.. Once i start to rev the motor above 10K RPM, the bearings make strange noise and seem to be overloaded. They also generate noticeable heat, which then transfers to the collet and chuck making then unbearably hot.
  • The motor generates some heat if operated at high RPMs for some time. Since there is not heatsink attached to the motor, i don’t think i would be able to operate it for more than five minutes continuously.

Possible improvements may include.

  • Bigger motor with some heatsink.
  • Bearing housing and outer body made of Aluminium.
  • Better collet and aluminium flex coupling.

I hope you enjoyed reading this article.. A video showing this tool in operation will be uploaded soon..

 

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