My initial tack was to create a 3D printed version. As I wanted to include the high speed option this needed a 24 tooth 5mm pitch pulley included. This did not print well.
Plan B was to buy a standard Bearing Boys 24 tooth pulley and incorporate this into the large diameter wheel. I modelled this in Fusion and concluded that perhaps a CNC aluminium part would be better. This would allow undercutting of the underside face of the pulley. This would not be possible using 3D printing as this would not be a supported area.
The stub axle that the pulley would revolve on protrudes 25.5mm from the BK3 side wall. The blade wheel groove needed to be 10.25 wide to accommodate the belt width. The retaining side walls needed to be 1.5mm wide. This totals 13.5mm width for the large pulley leaving only 12mm for the small pulley that would be needed for the highspeed set up.
This now became complicated in that the large wheel needed to sit around 5mm from the side wall to keep the belt in line with the motor drive pulley. A spacer washer was made for this. This left only 7mm width for the high speed belt and I needed at least 9.25mm just for the belt without retaining side flanges.
The light bulb moment was to realise that the high speed pulley could protrude beyond the stub axle without fouling the outer case cover. I could use the full depth of the pulley and counter bore the front face sufficiently to allow the axial retaining screw to hold the pulley assembly in place and allow free movement.
Here is a very much simplified sketch of the final assembly showing the counterbore for the retaining screw and the counterbore for the pulley boss into the large wheel. The small pulley and large wheel are locked together with 3 off radially spaced M3 x 10mm countersink head screws.
Here is a Fusion 360 graphic of the final pairing of the 24 tooth commercial pulley and the CNC machined large wheel. With hindsight the large pulley could be 3D printed by leaving the rear face completely flat rather than having a profile like the front face.
Parts needed to be bought in were obtained from Bearing Boys as follows : –
14-5M-25 (14 tooth, 5mm pitch,25mm tooth width) for the motor drive pulley.
24-5m-09 (24 tooth, 5mm pitch, 9mm tooth width) for the high speed pulley.
300-5M-09 (300mm, 5mm pitch, 9mm wide) 60 tooth belt for high speed operation
525-5M-09 (525mm, 5mm pitch, 9mm wide) 105 tooth belt for low speed operation
Note that all pulley and belt parts are to the HTD standard profile.
Here is the wheel in place with the belt set to run in high speed mode.
Note that I had one additional issue to address.
The aluminium wheel tended to not hold the blade centrally in the blade groove with the result that the teeth of the blade would rub against the wheel front flange. This did not happen in low speed mode when the blade runs on top of the drive belt. My solution was to fit a 160mm x 10mm wide elastic band in the wheel groove only when in high speed mode. The particular elastic bands are a standard size from Amazon and others. This solved the problem. There is no abrasive impact on the elastic band so life expectancy should be high and replacements are very low cost.
The above drive modifications in addition to the modified blade guide that I have detailed elsewhere, have given my BK3 not just a new lease of life but also a more accurate cutting capability. The effort has been more than rewarded and is to be recommended. If anyone needs further details please get in touch.
Some pieces of workshop equipment generate a sentimental attraction that is hard to break. One such piece of kit is my Burgess BK3 bandsaw which is ancient but has up to now worked reasonably well for my needs. I bought it on EBay from an owner in Lancashire and remember a nice day trip to collect it.
It is a very useful machine and gets pressed into use day in and day out. That is until the other day when the blade came off with a loud twang. On inspection the drive wheel had lost part of its blade outer retaining flange. It appeared to be very old brittle plastic and the damage was really to be expected given the vintage of the device.
After head scratching I designed a replacement edging strip in Fusion 360 which I 3D printed and glued in place. Fingers crossed that will give the machine a reprieve and extend its life.
In the course of looking for possible spares (no chance) I came across a reference to modifications to the BK3 in Model Engineer to improve the blade tracking and speed settings. (ME Vol 170 Issue 3944 and Vol 172 Issue 3962). The members of my local model engineering club came up trumps with copies of these articles for me.
The guide modification consisted of replacing the two stud guides with ball bearings. While the machine was in pieces it seemed like a good idea to implement this modification. The Fusion 360 3D model is shown below. The blade is sandwiched between the two ball races and these can be slid in and out and then be fixed in place with the cap head screws once the correct location is found to guide the blade.
I drew the replacement guide block assembly in Fusion 360 and milled it on the Tormach CNC from brass. The 1/2″ bearings came from BearingBoys.
All is now re-assembled and running really smoothly. The blade prefers to run in straight lines which is a revelation.
I have been avidly watching Clough42 on YouTube. James comes over as a really nice guy and his presentation of his projects is excellent.
My principle interest is the Electronic Leadscrew modification to lathes. When installed this removes all the hassle of gearboxes and look up tables to be able to cut both Imperial and Metric screw threads and to set X axis movement feed rates.
The concept is simple but his implementation is second to none. A rotary encoder is fitted to the spindle to count revolutions of the chuck and a stepper motor (or servo hybrid) controls the rotation of the leadscrew. The resulting feed speed is derived from look up tables. The whole installation is controlled by a Texas Instruments LaunchPad C2000 microcontroller development board.
I have documented how I implemented this on my Myford Super 7 Big Bore lathe and the pdf can be downloaded below. There is also a ZIP file of all the Fusion related models for either CNC or 3D printing.
We are sitting in quarantine and now on Day 5. Not really any different to how we were before we went to France and when we were in France – just different jobs around the house and workshop and zero outside contact other than food deliveries. (My wife gets very excited at the prospect of seeing the deliveries arrive).
I got fed up with the boot warnings on Fusion 360 that Win7 would not be supported so I decided that I would upgrade to Win10. My machine is fairly well spec’d so there was no great desire to upgrade to a new machine. It was i7 based and had 32MB of memory with a 250GB SSD and a 1TB secondary drive. Both drives were pretty full and into red warnings so I bit the bullet and opted for a clean load. I bought in a new 500GB for the operating system and app storage and a massive 2TB data storage secondary drive. Total cost under GBP100 which is staggeringly cheap.
Changing the hardware was simple. I bought in a SATA to USB dongle to allow the old drives to be available for data transfer and this made life a bit easier.
Loading Win10 and all my favourite apps took over a day. It is just never simple. Finding software keys is always a bit of a problem as some apps hide it away in Registry. Finding EXE loading files is another frustration. Why when you buy an app do some providers send you an email link to download direct with a licence key ? This results in nothing showing in ‘Downloads’ history to refer back to and reload the app. When you try to use the old email link it downloads the latest version and tells you that your licence key is no longer valid. When you go to their site the version that did everything you ever wanted has been upgraded and needs you to pay to now use the later version. ‘Hello .. I have paid for version X and I don’t want to pay for version Y thank you very much. Just give me a download link to restore what I know and love”. Rant over on that one.
Some weird effects on Outlook transpired. I have a GMail IMAP account and three POP accounts all loaded on Outlook. After loading I had an extra ‘Sent’ folder on the GMail folders tree which contained the Sent items from one of the POP accounts. Spent a lot of time on this and didn’t satisfactorily solve it other than deleting the contents from this duplicate folder. The messages are still there in the POP folder so not sure what that was all about.
My 3DConnexion Spacemouse loaded across fine onto Win10 but I still had a related exception error window coming up on booting the machine. This was the same as it had been on Win 7 so clearly something was common mode. I could click it and the message window would disappear but it was annoying. After some digging I traced it to Trend Antivirus. If I put the two 3dconnexions’ Windows folders into Trend as ‘Ignore’ items it all went away. Progress on that one.
So I think I now have a (mostly) stable Win 10 machine. I hate all the nanny state Windows ‘fluff’ that stops you getting quickly to things such as System\Hardware like it was in XP. In an attempt to ease this I have loaded Stardock’s ‘Start 10’ which mimics the old style Start menu and this makes me feel a bit more familiar.
Hopefully this was all worth doing and things will now go swimmingly along with no crashes and dramatic improvements in productivity …. gosh were those really pigs I saw flying past ?