dangerboy
Plastic
- Joined
- Mar 22, 2007
- Location
- Vancouver BC
I started this project by searching the forum and the web for anyone who had a similar experience and found nothing. Hopefully this will help someone in the future or give ideas to others.
The project started as approximately 60 spindles for a handrail in a high end house. The spindles were to be solid brass, 36” and 42” long, with the majority being 36” long. The five longer ones were to be sunk into concrete. The kicker is that the spindles are tapered, 1” dia at the bottom and 1/2” dia at the top. That’s a fair old taper for me. Couldn’t find anything indicating anyone else had done something like this, so started thinking. The job has to be done in a single cut, since any taper attachment must be fixed at one diameter. I did try a spring loaded steady finger to see if I could get enough support, that didn't fly.
If I could set the taper attachment just ahead of the cutter and pick the right insert or make a toolbit, then it should be possible. The customer wanted a proof of concept quickly, so I set up my two big lathes with the same setting on the taper attachments. Machined half of the taper on each lathe. That got me just 36”, my taper attachments being 18” long each. Of course this meant I had to blend the start and stop point which was a pain. However being a proof of concept, it just had to pass inspection by the designer and the homeowner. Size is not really an issue, just a really nice finish and even taper. The other point which the alert will have noticed is that the longer pieces wouldn’t work this way. So the answer seemed to be to make a longer taper attachment. I decided 48” would be enough, and bought a piece of aluminum flat bar and a chunk of cold rolled. The machine I was going to use was a Colchester Mascot 1600. The taper attachment is a dovetailed piece of tool steel, hardened and ground, with a 1/2” x 2” guide bar on the top that sets the angle. This all runs in castings bolted to the carriage. I decided for a short run that the aluminum would be good enough, sufficently lubricated. I machined the dovetail on the aluminum in two set ups, my mill not being long enough to do it in one. A pivot and two arcs for lock screws completed the aluminum. The cold rolled just needed filing and stoning to fit and holes for the pivot and the screws.
So far so good. Of course at this point, Murphy showed up. The customer and designer had decided they needed longer spindles. Oh and now there are 124 of them. So now they are 42” and 47” long. Just too long for my new taper attachment. Start again.
Same design, longer pieces. Six foot long this time. I decided not to machine the dovetails at this point. I sent the aluminum to a shop with a long bed mill and they did the dovetails in one cut. I figured this job had enough failure points and the dovetail could use a nice parallel cut. A few days later I have my new improved taper attachment.
Now the fun starts. The steady for my Colchester is a two finger style, with brass tips. I cut some test pieces and started. It was immediately obvious that this was not going to work. Chatter and vibration from the start. So, what to do. The steady from my Standard Modern was the three finger kind, but about an inch and a half too tall. OK I can work with that. I bandsawed the feet off and machined the bottom of the casting. Then machined the cut off pieces and made them so a standard thickness was missing. Cut some O-1 ground stock and drilled the holes so I could use the steady on the original machine again.
Back to the Colchester. Drill and tap holes in the carriage wings next to the original holes and bolt up the steady. OK new part. Better this time but still not what I need. So I’m thinking that the problem is not enough support, the tips on the steady being cone shaped and about 1/4” in diameter at the contact point. I decide to make new fingers for the steady, full 1” in diameter. I have some nice old bronze propellor shaft in stock, so that will be good and tough. After making these, I put a boring bar in the chuck set to 1” and bore the tips so they are on centre and good for size. Success! Perfect finish, even taper. Very pleased with myself. For one part. Halfway through the second, the vibrations re-appear. Now what? Lube. Must be the answer. Grease, moly, oil, Fluid Film, same answer. The tips were wearing out before I finished the cut. So I could nip up the screws but there was always some chatter or a line where the support was re-established. What to do?
The problem seems to be that the tips are wearing out on the long pass with lots of pressure. Lube doesn’t seem to be the answer, so harder tips. I come to the conclusion that bearings are the answer. OK more prop shaft and shortly we have bearing fingers. This proves to be the silver bullet. Solid finish, no wear and now nothing to do except shovel chips. I wanted to do this from the start, but time pressure from the customer and homeowner led to a sub-standard technique.
Now I expect some of you are screaming ‘hope you got time and materials!!!’. No such luck. Quoted job. So now you are screaming ‘yer an idiot!!’. Well yes, but not on this one. The quote was comfortably fat enough that I could go through these convulsions and still make out quite well. The point of this post is to hopefully help someone else who is stuck in some aspect of a job like this and not waste time and money that isn’t there. So in the end it was a rewarding job, but there were some sleepless nights trying to figure out how to do it.
Hope the wall of text helps someone out, and let me know if anything is unclear.
The project started as approximately 60 spindles for a handrail in a high end house. The spindles were to be solid brass, 36” and 42” long, with the majority being 36” long. The five longer ones were to be sunk into concrete. The kicker is that the spindles are tapered, 1” dia at the bottom and 1/2” dia at the top. That’s a fair old taper for me. Couldn’t find anything indicating anyone else had done something like this, so started thinking. The job has to be done in a single cut, since any taper attachment must be fixed at one diameter. I did try a spring loaded steady finger to see if I could get enough support, that didn't fly.
If I could set the taper attachment just ahead of the cutter and pick the right insert or make a toolbit, then it should be possible. The customer wanted a proof of concept quickly, so I set up my two big lathes with the same setting on the taper attachments. Machined half of the taper on each lathe. That got me just 36”, my taper attachments being 18” long each. Of course this meant I had to blend the start and stop point which was a pain. However being a proof of concept, it just had to pass inspection by the designer and the homeowner. Size is not really an issue, just a really nice finish and even taper. The other point which the alert will have noticed is that the longer pieces wouldn’t work this way. So the answer seemed to be to make a longer taper attachment. I decided 48” would be enough, and bought a piece of aluminum flat bar and a chunk of cold rolled. The machine I was going to use was a Colchester Mascot 1600. The taper attachment is a dovetailed piece of tool steel, hardened and ground, with a 1/2” x 2” guide bar on the top that sets the angle. This all runs in castings bolted to the carriage. I decided for a short run that the aluminum would be good enough, sufficently lubricated. I machined the dovetail on the aluminum in two set ups, my mill not being long enough to do it in one. A pivot and two arcs for lock screws completed the aluminum. The cold rolled just needed filing and stoning to fit and holes for the pivot and the screws.
So far so good. Of course at this point, Murphy showed up. The customer and designer had decided they needed longer spindles. Oh and now there are 124 of them. So now they are 42” and 47” long. Just too long for my new taper attachment. Start again.
Same design, longer pieces. Six foot long this time. I decided not to machine the dovetails at this point. I sent the aluminum to a shop with a long bed mill and they did the dovetails in one cut. I figured this job had enough failure points and the dovetail could use a nice parallel cut. A few days later I have my new improved taper attachment.
Now the fun starts. The steady for my Colchester is a two finger style, with brass tips. I cut some test pieces and started. It was immediately obvious that this was not going to work. Chatter and vibration from the start. So, what to do. The steady from my Standard Modern was the three finger kind, but about an inch and a half too tall. OK I can work with that. I bandsawed the feet off and machined the bottom of the casting. Then machined the cut off pieces and made them so a standard thickness was missing. Cut some O-1 ground stock and drilled the holes so I could use the steady on the original machine again.
Back to the Colchester. Drill and tap holes in the carriage wings next to the original holes and bolt up the steady. OK new part. Better this time but still not what I need. So I’m thinking that the problem is not enough support, the tips on the steady being cone shaped and about 1/4” in diameter at the contact point. I decide to make new fingers for the steady, full 1” in diameter. I have some nice old bronze propellor shaft in stock, so that will be good and tough. After making these, I put a boring bar in the chuck set to 1” and bore the tips so they are on centre and good for size. Success! Perfect finish, even taper. Very pleased with myself. For one part. Halfway through the second, the vibrations re-appear. Now what? Lube. Must be the answer. Grease, moly, oil, Fluid Film, same answer. The tips were wearing out before I finished the cut. So I could nip up the screws but there was always some chatter or a line where the support was re-established. What to do?
The problem seems to be that the tips are wearing out on the long pass with lots of pressure. Lube doesn’t seem to be the answer, so harder tips. I come to the conclusion that bearings are the answer. OK more prop shaft and shortly we have bearing fingers. This proves to be the silver bullet. Solid finish, no wear and now nothing to do except shovel chips. I wanted to do this from the start, but time pressure from the customer and homeowner led to a sub-standard technique.
Now I expect some of you are screaming ‘hope you got time and materials!!!’. No such luck. Quoted job. So now you are screaming ‘yer an idiot!!’. Well yes, but not on this one. The quote was comfortably fat enough that I could go through these convulsions and still make out quite well. The point of this post is to hopefully help someone else who is stuck in some aspect of a job like this and not waste time and money that isn’t there. So in the end it was a rewarding job, but there were some sleepless nights trying to figure out how to do it.
Hope the wall of text helps someone out, and let me know if anything is unclear.
