Michael G
25th Mar 2016, 07:49 PM
Today I intended to make up some gear blanks so I could make the change gears needed for the lathe to cut the screw for the angle plate project but when I pulled the cover off I saw that I'd left it set up to do something else...
One of the guys at work is a car enthusiast or more correctly an engine enthusiast (what funny hobbies some people have - not something sensible like restoring and using fifty year old machine tools:U)
He had been given the patterns and raw casting for some inlet bell mouths but they had been mis-drilled so wanted to know if I could help him get them to a usable condition for his next engine build...
(these sit inside the air plenum and guide the air to get a laminar flow through the carbies. Being for a V8 there were 8 of them - and of course they needed to be more or less identical so that the air flow was all the same)
The castings were pretty ropey (as you will see later) and 3 had been drilled for mounting holes but almost a random hole placement - no marking out or jig drilling here. First order of business was to plug up the drilled holes. The normal way of doing this is to counter sink the hole and then fill with weld. These were Al but the same method applies so out with the TIG and away we went. Ideally you go from one side and then repeat from the other so that there is complete fill but the placement of the holes made that difficult - I had to come back later and re do one casting to get better fill. Al castings can be tricky as the alloys that cast well sometimes don't weld or machine well, but these were alright - makes me wonder what they actually are.
361732
The castings had been linished on the base to make them flat but as this was an air intake ideally the bore of the bell mouth should be square to the flange and the axis of the bore should be the datum that all other features were relative to. Locating on the bore was difficult because the core used to cast was not properly located but eventually I hit on the idea of 2 discs that would locate snugly in the bore. First step was to make that tooling up and a wooden yoke to hold the casting against the disc so that the bottom flange could be faced and the outlet sized.The yoke locates on the two hold down bolts either side of the mount. Clean up as shown in the second photo (your eyes are not playing tricks - the flanging is not even symmetrical)
361731 361730
In that second photo you may just be able to make out the mismatch in the core pattern has not allowed uniform cleanup. Note that if I was planning on doing these again the tooling would be from metal but as it is wood does the job. Once those two features were machined, I could hold the casting onto the form with a special plug and the tailstock.
361729
Because all 8 needed to be the same, I decided to set up to do a cut (the three being face the other side of the flange, turn the OD of the flange, trim the casting to length), locking the respective axis so the distances were the same and swapping through all 8 castings before changing to the next setup. As you can see from the clean up cuts I was doing, these things were just not uniform well made castings! My advice to Paul (the requester) would be to bin these patterns because they produce castings that are all over the shop. I suspect that machining from a piece of bar stock would be just as fast as every surface is going to have to be trued up.
361727 361728
Now the tricky bit - cleaning up the outside. I needed a copy attachment ideally but don't have one so I tried tracing against a 1:1 plot. The basics are shown in the photo below. The white piece of paper held on the tail stock with magnets is a plot of the profile I wanted. I have used a mag base indicator on the compound as a pointer ('cause I could not find anything suitable and could not make anything without breaking set up:doh:) I engaged a slow longitudinal feed and used the cross feed wheel to keep my 'pointer' on the line in the plot. I used a rounded HSS tool so the changing cutting point did not matter, but it worked very well. A bit of polishing with emery and WD40 and they looked the part - certainly better than the sand cast finish they came in
361726
The result so far.
361733
Still to come - repeat the tracing trick on the inside, drill the mounting holes (drill jig already made - it's just visible on the toolbox. Locates in the main bore the holes are in line and symmetrically placed) and trim the edges of the mounting flanges.
Michael
One of the guys at work is a car enthusiast or more correctly an engine enthusiast (what funny hobbies some people have - not something sensible like restoring and using fifty year old machine tools:U)
He had been given the patterns and raw casting for some inlet bell mouths but they had been mis-drilled so wanted to know if I could help him get them to a usable condition for his next engine build...
(these sit inside the air plenum and guide the air to get a laminar flow through the carbies. Being for a V8 there were 8 of them - and of course they needed to be more or less identical so that the air flow was all the same)
The castings were pretty ropey (as you will see later) and 3 had been drilled for mounting holes but almost a random hole placement - no marking out or jig drilling here. First order of business was to plug up the drilled holes. The normal way of doing this is to counter sink the hole and then fill with weld. These were Al but the same method applies so out with the TIG and away we went. Ideally you go from one side and then repeat from the other so that there is complete fill but the placement of the holes made that difficult - I had to come back later and re do one casting to get better fill. Al castings can be tricky as the alloys that cast well sometimes don't weld or machine well, but these were alright - makes me wonder what they actually are.
361732
The castings had been linished on the base to make them flat but as this was an air intake ideally the bore of the bell mouth should be square to the flange and the axis of the bore should be the datum that all other features were relative to. Locating on the bore was difficult because the core used to cast was not properly located but eventually I hit on the idea of 2 discs that would locate snugly in the bore. First step was to make that tooling up and a wooden yoke to hold the casting against the disc so that the bottom flange could be faced and the outlet sized.The yoke locates on the two hold down bolts either side of the mount. Clean up as shown in the second photo (your eyes are not playing tricks - the flanging is not even symmetrical)
361731 361730
In that second photo you may just be able to make out the mismatch in the core pattern has not allowed uniform cleanup. Note that if I was planning on doing these again the tooling would be from metal but as it is wood does the job. Once those two features were machined, I could hold the casting onto the form with a special plug and the tailstock.
361729
Because all 8 needed to be the same, I decided to set up to do a cut (the three being face the other side of the flange, turn the OD of the flange, trim the casting to length), locking the respective axis so the distances were the same and swapping through all 8 castings before changing to the next setup. As you can see from the clean up cuts I was doing, these things were just not uniform well made castings! My advice to Paul (the requester) would be to bin these patterns because they produce castings that are all over the shop. I suspect that machining from a piece of bar stock would be just as fast as every surface is going to have to be trued up.
361727 361728
Now the tricky bit - cleaning up the outside. I needed a copy attachment ideally but don't have one so I tried tracing against a 1:1 plot. The basics are shown in the photo below. The white piece of paper held on the tail stock with magnets is a plot of the profile I wanted. I have used a mag base indicator on the compound as a pointer ('cause I could not find anything suitable and could not make anything without breaking set up:doh:) I engaged a slow longitudinal feed and used the cross feed wheel to keep my 'pointer' on the line in the plot. I used a rounded HSS tool so the changing cutting point did not matter, but it worked very well. A bit of polishing with emery and WD40 and they looked the part - certainly better than the sand cast finish they came in
361726
The result so far.
361733
Still to come - repeat the tracing trick on the inside, drill the mounting holes (drill jig already made - it's just visible on the toolbox. Locates in the main bore the holes are in line and symmetrically placed) and trim the edges of the mounting flanges.
Michael