Workshop Tooling – Page 3 – Woody's Workshop

July 29, 2023July 29, 2023

Workshop air compressor problems

Understanding what was happening and why

I have a Bambi PT50 air compressor in my workshop. I chose it on the basis of being relatively quiet and having the capacity to provide sufficient air for my Fogbuster coolant system while working within the compressor’s specified duty cycle. The PT50 has dual compressor motor pumps.

The PT50 works very well. It is an oil free compressor and only needs the moisture bleed as a regular maintenance activity.

Of late I ran into an issue with air leaking from under the Condor MDR1 controller. This led to an investigation of how the compressor control process works, something I had not given much thought to while the unit was working fine.

The process, when working properly, is that the compressor motors push air into the air reservoir (tank) via a non return valve (NRV). When the pump stops the NRV seals the pump feed into the tank. The air contained can then only exit the tank via the MDR1 controller. When the air pressure in the tank drops due to demand and to a defined level (set by the controller) then the pump kicks in again and tops the tank up. A simple looping process.

The controller has a rubber diaphragm that expands and retracts subject to the pressure level in the tank. This diaphragm pushes on a hinged plate that acts as the trigger for the electrical switch that turns the pump motors on and off.

There is a secondary process to this.

When the pressure level in the tank reaches the point where the pumps need switching off, the NRV closes but there still remains a high pressure in the feed pipework from the pump to the NRV. This pressure will put stress on the pump motor when it next tries to start up. In the extreme this back pressure could cause a pump motor to stall.

To overcome this there is a tiny bleed valve in the controller that gets triggered to open simultaneously with the point where the pump switches off. The bleed is triggered by the same hinged plate mentioned above. The bleed valve is connected via a small tube that tees off the NRV in the feed from the pump motor. When triggered the valve vents the high pressure in the pump feed pipe to the NRV. This cause the sudden burst of air you hear when the pump switches off at its high pressure trip point.

So onto the problems that might occur.

The NRV seal can become damaged or worn or contaminated with debris from the reservoir tank. This means it will not seal when the pump switches off and the air in the tank will vent back out past the NRV, pass along the thin tube feeding the bleed valve and manifest as a continuous rush of air similar to the ‘switch off burst’ mentioned above. To summarise the fault – the pump switches off and you hear air continuously escaping. Solution – NRV valve damaged or contaminated and therefore not sealing. Check, clean and / or replace the valve.

The second problem is where there is air escaping from under the controller but only when the pump is running. (It is important to note that this does sometimes occur naturally when the pump is first switched on with an empty tank. In this situation there will perhaps not be enough pressure at switch ON to close the NRV. Once a few seconds of pumping has occurred the NRV should close). If the air continues to leak from bleed valve under the controller with the pumps running then this means the tiny needle that activates the bleed is either jammed with debris or the diaphragm / hinge plate in the controller is damaged. Note that on the MDR1 you can remove the valve to check it. The valve is enclosed within the black body of the bleed pipe mounting gland. It is twist locked in position.

In summary therefore : –

Air escaping from under the controller when the pump is not running suggests the NRV needs checking and / or replacing as needed.

Air escaping from under the controller when the pump is running suggests a problem with the needle bleed valve or the diaphragm / hinge plate in the controller. This is a more serious problem. It will cause the pump motors to overheat while trying to deliver air that is continuously escaping from the bleed valve. The MDR1 is not user repairable and is a crimped sealed unit. The picture below shows the MDR1 internals and the NRV.

The first glance the cost of replacing the NRV or the MDR1 controller will appear similar but do take time to shop around. Replacing either of these will involve disconnecting various associated pipe fittings. As ever, take a picture before you start disassembling. Thoroughly clean all the parts before re-assembling. Use a sealant such as Loctite 577 to achieve quick and easy air tight seals.

Finally a word of warning – compressed air is a dangerous medium. Before undertaking any remedial work on a compressor you must ensure that the reservoir is fully vented and empty.

Links to similar or related post are listed below : –

July 17, 2023July 17, 2023

Replacement Cowells Chuck Key (Part 2)

Sintered Tool Steel Experiment

Some while ago I posted about my experiment in reproducing a Cowells ME lathe chuck key as it seemed there were a few owners with broken teeth on their keys.

Since then I have received a number of requests for replacement keys which I have tactfully declined. They are not the easiest of things to reproduce and a potential for broken tooling.

I use PCBWay for my production PCBs and I recently noticed that they can produce sintered 3D objects from a STL file. They offer various materials for this process. Out of curiosity I sent the STL file for the chuck key to them and ordered 5 pieces in sintered tool steel. Twenty days later I received 5 chuck keys. They look good and they match my dimensions and more to the point they work in the chuck. I have no experience on how strong sintered tool steel might be but this video from My Tech Fun is quite impressive.

My Tech Fun

The downside of course is that they were not cheap (~£50 each, heavily thumped by courier costs) but if you have a Cowells and the frustration of a chuck key with a broken tooth maybe this is a reasonable price to pay. Let me know quickly if you are interested in buying one otherwise I will put them on EBay.

Links to similar or related post are listed below : –

April 17, 2023April 17, 2023

Illuminated Optical Centre Punch

A variation of a recently published design

There was a feature in a recent engineering forum by Nell’s Mechanical Man Cave regarding a 3D printed Optical Centre Punch. The design had an angled magnified side window allowing the viewing of the punch point. This conveniently allowed viewing of the point without having to swap out the viewer lens.

The author was offering a free download of the STL files for the punch body and also two versions of a base print. I made contact and received the print files and duly printed out the body and base models.

To get a better understanding I suggest you view the YouTube post on the following link :

My immediate impression of the design was positive with the only drawback being the limited light available inside the punch body when trying to align the punch point.

I started a dialogue with Neil and suggested to him that the addition of LED lighting inside the punch body might solve this problem. Neil was positive and supportive of the suggestion and the result is detailed below.

I re-modelled the punch in Fusion 360 and after some experimentation decided to mount two white light LEDs inside the dome of the body with the associated battery and switch mounted in the top surface of the body under a removeable cap. Here are a couple of visual views out of Fusion.

You can download my full write up and updated STL files from the following ZIP file link.

optical-centre-punch-STL-and-PDF Download

Links to similar or related post are listed below : –

January 6, 2023August 11, 2023

Gack Vice as a 3D Print

A possible light duty clamping solution

I came across the design of a Gack machine vice on a metalworking forum. This is a two part vice that picks up on the tee slots in a mill table to allow an infinitely variable clamping width within the limits of the table dimensions. It is ideal if a part needs to be skimmed flat over a wide area. The item to be machined is clamped by an adjustable jaw against a fixed jaw and is supported by parallels as needed.

The grip tightening adjustment is done with a ball bearing pushing centrally on the adjustable jaw with a M10 cap head screw and the gripping jaw hinges downwards on two dog point grub screws. Here is an image of my interpretation of the concept. My aim was to create a vice that would be able to be mounted on my M8 tooling plate which has holes on a 25mm matrix or directly on the milling table tee slots which are spaced at 50mm.

I modelled my version in Fusion 360 and below is the Fusion exploded view.

The metal side plates are to increase the strength of the two hinging pivots of the clamping jaw.

The idea works well for light skimming jobs but would not be suitable for large depths of cut.

If you want a really robust version then you could replace the PLA print with a metal equivalent or you could buy a kit from Hemmingway Kits but their castings restrict the use to tee slot mounting only.

Click here to download a ZIP file containing my full write up, 2D drawings and the 3D STEP file.

UPDATE: – Since the original post I have updated the design to a totally metal version. The static jaw is now much easier to fabricate using a piece of angle plate. The mounting slot dimensions are specific to my M8 x 25mm matrix tooling plates.

Links to similar or related post are listed below : –

October 7, 2022October 19, 2024

BK3 Bandsaw Lazy Susan Turntable Update

Adding a Rotation Stop Pin

There is no doubt that adding the Lazy Susan rotating base to my BK3 Burgess Bandsaw has been a good move. Being able to adjust the orientation of the BK3 to suit the material being cut makes life so much easier.

The one issue that has come to light is when adding heavy pressure to the cut I was having to push the material with one hand while trying to stop the BK3 rotating with the other hand/arm/knee.

Following one such episode I have added a stop pin that locates into preset holes in the new wooden base. I used one of the four unused holes in the original BK3 baseplate as the pin locating point. These holes are 6.5mm diameter (probably 1/4″ originally). I could have used a 6.5mm rod pushed through one of these holes into the new wooden baseplate but the BK3 baseplate metal is only 2mm thick. This would probably have resulted in a sloppy hold. Instead I made a small boss and fastened this into the BK3 baseplate left rear hole. The boss clamps on the underside of the baseplate and is held in place with a M6 nut and washer. The 3.5mm through hole provides a rigid guide for the locking pin. The sketch for the boss is below.

The four original holes in my baseplate were a bit rough and the one I chose to use needed a deburr so the shoulder on the boss sat flush to the bottom side of the BK3 baseplate.

The new wooden baseplate needs to be removed from the Lazy Susan so the boss can be mounted in place. Once the boss is in place the Lazy Susan is refitted. A 3.5mm rod is lightly hammered into the wooden baseplate to mark the desired lock positions. The Lazy Susan is then removed again and the wooden base drilled through at the marked locking positions.

The locking pin is a length of 3.5mm silver steel (drill rod) bent at right angles with its ends nicely rounded. The rod is ~45mm on the locating length and ~25mm for the grabbing handle. Here is an image of the finished construction.

This simple modification works extremely well and with hindsight should have been in my thinking when I first fitted the Lazy Susan.

A full list of my BK3 modifications are here

Links to similar or related post are listed below : –