I had a need to run an armoured cable down a duct to an outbuilding. The duct had thoughtfully been installed a long time ago with the potential for use in the future.
The future arrived and it was a daunting cable run of over 25m. Armoured cable is pretty rigid which helps on the straight runs but when it comes to bends in the duct it had a mind of its own.
After struggling for some time I had the thought that some form of leader was needed to navigate the bends. After searching the workshop I decided a cable tie (zip tie) might be rigid enough but flexible enough. I snipped the fastener ratchet block from the tie and taped the residual length to the end of the cable as below.
A liberal coating of DC4 silicon grease and the cable shot down the duct and round the bends like a rat up a drainpipe.
It arrived today after nearly a month in transit due to the current lock down restrictions. On opening the package I was impressed with the quality of the engineering. It is a nice device. It uses the usual 3 pronged contact mechanism. Supplied with the probe is a tube of grease that helps protect the contact reliability. The interface cable has a 5 pin DIN that plugs into the Tormach expansion socket and the shank is a standard TTS compatible size.
I ran through the initial preparatory procedure and then loaded it into the Tormach 440 spindle. Pathpilot has a number of excellent set up routines to adjust the probe and make measurements. One of these, the Effective Tip Diameter is quite critical. All this went to plan and very quickly. Some initial probing gave repeatable and accurate results so first impressions are good.
I’ll give some updates as the probe gets pressed into service but my first impressions are good with repeatable accurate readings.
In the course of checking out the ITTP probe I needed a reference cross check on the various setup measurements. My Haimer Taster seemed a bit erratic and on inspection I discovered the axial shank holding bolt had worked lose. This meant a re-calibration of the eccentricity of the probe point would be needed.
The alignment process involves adjustment of four grub screws in the shank body. These tweak the ’tilt’ of the shank to get a concentric rotation of the probe ball point. As there are four screws I use two hex Allen keys to make the adjustments to each in line pair. This is quicker than with a single hex key being swapped from side to side. It is a bit like the process I use when centring a 4 jaw chuck. The adjustment is done against a dial gauge riding against the probe ball point. Once you get the knack this process doesn’t usually take too long using the two key method.
The frustration is that the Allen keys provided with the Haimer are a bit chocolate based and the ends chew up easily. The result is you tighten a grub screw and the hex key end twists and gets jammed into the hex socket in the grub screw. While trying to waggle the jammed key you mess up your carefully made adjustment. Aaaargh !
I ground back the worn end of the Allen keys to clean up the hex profile but they quickly degraded. In the end I took the grub screws out completely and replaced them with some M4 cap head bolts. Joyful !
Yes I know it doesn’t look pretty but it is now a real pleasure to make the adjustments with a couple of larger T wrenches. It is probably a criminal thing to do to such a lovely instrument but life is too short.
At last a 4th axis drive for the Tormach PCNC440 !
I have waited 4 years for this to be available and did not hesitate to put in my order to Tormach for one of the new MicroArc drives. Probably the best way to get a good idea of this product is to watch John Saunders’ video.
The MicroArc wasn’t a low cost buy and because 4th axis was not around when my 440 was originally shipped, I needed a fitting upgrade kit as part of the order. Having placed my order with Tormach it took exactly 7 days for DHL to arrive on my doorstep with the shipment. Quite amazing considering the difficult times we are experiencing at the moment.
It took me about one hour to fit the new stepper driver and additional wiring. As ever there were good clear instructions from Tormach. I switched on the 440, enabled the 4th axis in PathPilot and I could control the A axis from the PathPilot screen. Very impressed.
I watched John Saunders video on the MicroArc and how to do 4th axis programming in Fusion 360. I drew up a simple model in Fusion but could not get it to produce working GCode. I had some comms with John and he gave me some pointers. The model had a rotational repeat pattern but while I could run a single op code, if I tried to run the rotational pattern the post processor came up with an error message and would not output any code.
I thought at first it was because I was only using a Fusion hobbyist licence and that 4th axis maybe was not possible. A really helpful dialogue with Shannon McGarry at Fusion cleared up that issue so it must be something else.
After some experimenting I discovered that you have to set the axis of rotation in the post processor dialogue options list. All then worked fine.
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.
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.
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.
My wife has presented me with a sign that has just got JSN written on it. It is to remind me when I answer the phone to a ‘can you just do’ enquiry…… to Just Say No.
I try my best to live up to her expectations but sometimes something comes along that should really be a JSN job but which scratches an itch. You know what I mean. You think about it and you do all the right mental arithmetic in your head and the answer keeps coming back to the same – don’t even think about it. But the the other side of my brain is screaming at me … what a challenge, what a learning experience, what fun to have a go at it. Providing the asking party is aware of your thought process or lack of it and accepts that it might just go belly up and never come to fruition then why not ?
Back to the story – 10 days or so ago I had a call from David Pawley who is a turret clock expert extraordinaire to say someone he knew was after an escape wheel for a turret clock and was desperate. David passed on the details and a couple of days later the potential customer arrived on our driveway. After a suitably socially distant conversation and a rubber gloves inspection of the old damaged wheel …. I got sucked in and turned the JSN sign over to face the wall.
The Brocot is no ordinary escape wheel. In fact it is a real challenge. Not a simple fly cutter job. Traditionally it would be cut in an indexing device such as a lathe with two different cutters, one for the curve and one for the notch. I didn’t have these so I thought I would probably upset the traditionalists and try to use CNC.