The Cowells Model Engineer miniature lathe is very popular in home workshops. It is a well made machine and very accurate to use.
There appears to be one recurring problem with the design and that is the chuck key for the TMC3001 3 jaw chuck often ends up with broken teeth. To understand this better you need to be aware that the Cowells chuck does not have a standard style chuck key. It is more like a drill press chuck key as you will see from the image below. It also has 12 teeth which is unusual compared with drill press chuck keys which usually have 11 teeth. Using too much strength trying to over tighten the chuck rotary mechanism could lead to severe machinist depression.
Cowells 3 jaw chuck and chuck key
I have to admit this is going to be another JSN job that slipped through the net while the sign had been left facing the wall from the last one …. a client wanted to know if I could make a replacement chuck key.
It seems that these are not readily available as replacement parts. So another little challenge was beginning to niggle at me. I thought about try to use Fusion 360 to create CAM for my Tormach PCNC440 CNC mill it but it didn’t feel like the right approach. There had to be an easier way.
While siting in the sunshine at lunch time (probably not paying attention to what my wife was telling me …. (again) …. ) I wondered if standard wheel cutting techniques could be used. This would mean a custom made fly cutter which didn’t fill me with joy and suggested a lot of grief. I then wondered if a standard clock wheel cutter might fit the same profile as the chuck key teeth.
With lunch over I dug out my treasure trove of PP Thornton wheel cutters and compared them with the profile of the chuck key. The PP Thornton 0.95-7 modulus one looked a good bet as a match. In its normal life this would be a 7 tooth pinion cutter.
The idea looked like it might work. I measured and sketched up the rough dimensions of the chuck key head profile which is shown below. For ease of making a proof of concept prototype I decided to use aluminium.
First job was to profile the aluminium stock to the outline shape of the chuck key. This completed I then mounted my Sherline CNC rotary table in the mill table vice and with some jiggery pokery managed to get the vice / table aligned at 14 degrees (90-76) to the X axis movement. I set the centre line of the pinion cutter with the centre line of the aluminium profile. I dialled in 12 steps on the Sherline and began cutting back and forth.
To match the original teeth depth I had to go down to the full depth of what the pinion cutter profile would allow. On the prototype I didn’t bother finishing the shank of the key and below are some process images and the final prototype result.
Images of the process and final result making a prototype Cowells lathe chuck key replacement.
The prototype worked. I just have to make a fully finished steel version …… oh and remember to turn the JSN notice back over so I can’t miss seeing it next time an intriguing enquiry comes in.
Update : – Silver steel ruined my cutter … they are really meant for brass. Looks like it will have to be a CNC method.
I had been using Hall Effect devices to modify my William Smith Gearless Gravity Arm clock and had been surprised by their ease of use and repeatable trip points. (More about this to follow in a separate post).
I had also been frustrated with my inability to set tool heights reliably in PathPilot despite using various methods all of which didn’t want to agree with each other.
This resulted in the construction of a Hall Effect based Tool Height Setter that appears to solve the problem. The write up is lengthy so I have committed it to PDF for download but here are a couple of images to give you an idea of the result.
A simple cross section sketch of the tool height setter concept using a Hall Effect sensor
Finished tool height sensor mounted on the PCNC440 milling table
I recently had a job to do where I needed to see and measure a very small part I was making. The simple microscope was struggling to cope or at least I was struggling to cope with it. Looking on the net to see what the current technology could offer I spotted a device on Amazon that looked interesting.
It was a bit more expensive but nowhere near a ‘proper’ professional optical product. Having taken delivery it is very impressive.
It can act as a simple standalone viewer using the built in screen or can be externally connected via HDMI to a monitor or (and this is the impressive bit) it can be connected to a PC via a superb application that has so many bells and whistles it will take me ages to understand all the functions. The sensor is a 16 Megapixel Sony CMOS 1/2.3″ HD device and video output can be 4K/2k/1080P. Magnification is up to x300.
So I am well pleased with the investment and it will certainly earn its keep.
I recently bought a special offer price tool height setter from Banggood. On arrival this seemed nicely made and robust and looked like a worthy addition to the armoury.
The Tormach PathPilot control software has facilities for tool height setting using such a probe. I also have a Wildhorse Innovations probing tool for edge and centre setting. Both these devices can be connected to the Tormach PCNC440 external input accessories connector which is a 5 pin 180 degree DIN.
The input to the Tormach accessory socket is a 2 wire connection. Sensing and operation of external tools like the probe and tool setter depends on the device having a normally closed connection that goes open circuit when activated (i.e. the probe tip moved or the tool setter pushed down). The probes are in essence a single pole normally closed switch.
Frustration Sets In
After spending time having to keep swapping these two devices in and out of the accessory connector I figured there must be a better way.
The Tormach does not care if you connect multiple probes at the same time provided they are all in series on an electrical loop to and from the two pins on the interface connector. Any device when activated will break the loop and create an interrupt to the PathPilot software. Because you will be in the area of PathPilot software that relates to the function you are measuring, the relevant probe will be the one you are intending to use.
The Solution
What was needed was a simple interface box that allowed the two probes to be connected in electrical series back to the two pins on the DIN connector. I also wanted flexibility to be able to unplug either of the two probes and not affect the operation of the other. This meant that on removal of either probe it would need an electrical short circuit across the pins of the connector from which the tool had been removed.
This could be done with a small by-pass switch, that is normally open circuit, connected across the connector. You would manually close this switch if the probe is removed.
This is fine so long as you remember to activate the switch when you remove the probe otherwise the sensing loop will see an open circuit and the software will get confused.
My solution was to use sockets for the connections that would automatically provide a short across their contacts when their mating plug is removed. A good example is an audio style jack plug socket. These come in various sizes (2.5mm, 3.5mm, 1/4″ etc). Usually on these sockets the tip of the connector gets shorted to another contact when there is no mating plug in place.
I had some 3.5mm stereo jack plug and sockets to hand (either mono or stereo can be used as it is only a two wire connection) and these were simple to wire for this application.
I also ran a modified version of one of my standard 3D printed enclosures to mount them in and fitted a flying lead to a 5 pin DIN to plug into the Tormach interface. A hot glued magnet onto the bottom of the enclosure allowed flexible mounting of the box somewhere on the Tormach body. The only fiddly bit was replacing the existing connectors on the two probes with a 3.5mm jack plug. (Don’t forget to the put the connector shell on the cable before you solder the wires in place ….. ).
A neat solution and the problem solved. Both devices plug into the box to perform their various probing functions into PathPilot. Unplug one of the probes and its mating socket will automatically short out the probe connections when the plug is removed. The remaining probe plugged into the other socket will continue to function.
We got the electric bill for last winter and there was a sharp intake of breath … maybe the fan heater had been on too much in the workshop and maybe I did forgot to switch it off once or twice when going to bed … something had to change.
I did some research on diesel heaters as used in motor homes and commercial vehicles and the concept looked like it would meet my needs. I did some calculations on the workshop volume I needed to heat as an empty shell. With my insulation and window content this came to a figure of 3kW. Searching on EBay revealed lots of kits and ready built units so my first thought was to order a ready built one. This duly arrived and I decided to run it up to see what happened.
Actually nothing really happened.
The fan came on ran for a few seconds and then the unit shut down. The controller was showing a severe droop on the supply volts even thought the PSU was rated at 10A. More web reading and comparing notes with other users revealed these units take a serious current surge at switch on while the glow plug is warming up. If it sees a voltage droop it thinks it is in a vehicle and switches off to protect the vehicle supply.
Bigger power supply acquired and plugged in. Still no joy. I then realised I needed to prime the fuel line. Quite a few clicks of the pump later I had a full pipe feeding the device and finally it ran up. The fan was flat out and the pump was clicking like a French grenouille on heat.
And what a stink it made. I guess it was burning off all the manufacturing oils but it was pretty acrid. Finally the fog cleared and I could see the neighbours house and we had heat. Quite a lot of heat. Fiddling with the pump rate brought the heat and the fan rate down and all seemed good. But it was noisy.
There now followed some serious navel contemplation. Did I really want this fire breathing Smaug inside the workshop ? Not really. So how to solve the installation ?
Immediate thought was to mount the unit external on the side wall and feed the warm air from the unit into the workshop and take in air from the outside to warm. The smelly exhaust inlet and outlet would also then be outside. Not a good idea taking outside air and warming it unless I wanted a very rust rich environment.
So air would have to circulate from the workshop, get heated and blown back inside. This means two 80mm holes in the workshop wall plus a power and controller wiring duct of say 20mm. A plan was forming and I could see where the two air ducts could be located.
Next problem the (I have to say very horrible) enclosure my ready made heater came in would not protect the contents nor would it last very long sat in the outside air.
Empty original enclosure after stripping components
New Enclosure
Much Fusion 360 playing later I had a design based on a 20mm angle iron frame and aluminium sheet covering.
Original Fusion 360 model of the enclosure frame less the two top bracing steels
The angle iron and sheet were ordered from Aluminium Warehouse and came very quickly. I was now going to have to grasp the nettle and refresh my TIG welding knowledge to create my first major TIG construction. (I only have TIG as MIG scares the **** out of me).
Even though I say it myself I was pretty chuffed with the frame that resulted. Some of the welds were far from ticketable but my angle grinder and Hammerite paint soon covered up my ineptitude.
TIG welded heater angle iron frame after clean up and painting
The aluminium covers also stretched my resources as I don’t have a formal metal bender but I do have some very long lengths of angle iron and a robust vice. Two side walls, a front panel and drop on top cover resulted without any serious clangs. Loving it.
The return air inlet needed an interface of some sort so a Fusion model was created and printed (6 hour print …).
3D printed diesel heater 80mm air inlet cowl which took 6 hours to print
With the enclosure complete, I mounted all the components and ran it up again. The new power supply also failed to do the biz so I decided to go with a meatier version inside the workshop rather than inside the external cabinet.
Installation day loomed. I was very ably assisted by Dave who is a long time friend. We are both cut from the same engineering mould and we usually end up with an interactive plan of action.
First job was to cut the hot air duct hole in the workshop wall. We had a long pilot drill, an EBay 80mm cutter and a SDS drill. Serious grief. The workshop outside brickwork seemed to have a Titanium content. We finally broke through into the cavity and thereafter the inner Thermalite block was like cutting chocolate cake in comparison. First hole finished and more to the point in the correct position.
We now offered the unit to the wall to match the routing of the hot air outlet pipe of the heater. We put a car jack under the unit to keep it in position while we drilled the mounting holes. Holes drilled, we then mounted it on the wall and drilled the cable duct and lined it with a piece of uPVC water pipe.
Re-boxed diesel heater enclosure mounted on the workshop outside wall. The pumps is enclosed in some foam to deaden the clicks.
The circulating return air from the workshop was to come through the workshop wall and back to the heater from just over a meter away. I had a suitable length of 80mm spiral metal ducting for the air return and a mating right angle joint to route this through the wall. We marked off the duct hole position and drilled out a second 80mm hole (more grief, less dust as we damped it down, and hammer and chisel when we got fed up with the useless 80mm cutter).
The Cunning Plan
I didn’t want the metal spiral ducting exposed to the elements and also saw it as a source of heat loss. There is no point in heating up the workshop and then send the warmer air outside to lose heat on its way back to the heater. The solution was to buy a standard 1m length of 110mm soil pipe and a right angle joint with two mounting clips from Wickes. We wrapped the 80mm spiral duct in bubble wrap (quite a few turns) to fill the space inside the 110mm soil pipe to make a coaxial structure. As luck would have it the spacing to the wall of the soil pipe was pretty much ideal to use the standard pipe clips. We did however have to cut down the right angle soil pipe connector to get it flush to the wall. It then got a dose of squirty foam to seal it.
Finished diesel heater enclosure with coaxial inlet duct using 110mm soil pipework and fittings. The 80mm internal duct is wrapped in bubble wrap.
We were both very pleased with the result. As Dave commented it looked better than a professional install would have done.
This was the bulk of outside work done apart from mounting the exhaust inlet and outlet pipes. Inside we had the hot in wall vent grill to fix and the controller wiring.
I still haven’t decided where to route the outward air duct but currently it sits sucking air from under the Myford Super 7 cabinet. I am not comfortable with this (the location rather than the potential draft around my ankles) as it will tend to suck up workshop dust and particles. Some form of filter will be needed. As yet I haven’t mounted the new power supply on the inside wall.
We ran it up and I can describe it as toasty warm. At least one good reason to look forward to winter, probably the only one.
Finally thanks to Dave for helping. Also thanks to Steve Niebel for detailing his experiences with a similar unit.
If you want to know more about the heaters then the best source I found on YouTube was Dave McK 47
Anyone wanting a very basic indoor housing for their heater components should send me a message ….. and soon …. otherwise it is going in a skip (but I might save the handles).
