bogmonster
Established Member
Hi,
I have been looking for an easier way to hold work to finish the bottom of bowls and the like. Don't particularly want to open the debate on whether this is necessary or not, just my personal preference. Anyway, I have used the tailstock method with a friction drive and this works OK with a couple of drawbacks: Access is difficult to the centre and only works for stuff that fits over my lathe bed (no use outboard). So I also used a ring (doughnut) chuck and got on well with it but it is a little scary with wing nuts flying around. This is still a solution I use occasional if my preferred solution, the vacuum chuck, isn't suitable.
I decided against Cole jaws and the Longworth chuck. I have heard mixed views on the longworth and the commercial cole jaws are not cheap and they are not suitable for natural edge. That left me with the idea of the vacuum chuck – nice but potentially very expensive.
Anyway, this is a short description of my vacuum chuck build. I have added it here because the design is slightly different to some of the others I have seen but with lots of blatant copying as well from folks like Bob Chapman (thanks Bob). Might give people some additional ideas. The overall cost was about 60 pounds – didn't keep a full bill of materials and has a few odds and sods to start with. I decided I wanted to use a proper vacuum pump, not a vacuum cleaner as this will give a better results on a small chuck. There is absolutely no reason a vacuum cleaner can't be made to work and indeed I did make up the chuck first and tried it with my wimpy shop vac and it worked – sort of. This was on a 4” chuck so I think would have been fine on a bigger chuck, say 8”.
The chuck is very similar to Bob's with an MDF base (must be sealed) and a soil pipe. For a gasket I use a lose disc of laminate floor underlay. The main difference to other solutions I have seen if the rotary adapter and pulling the vacuum through the spindle. My lathe has a hollow spindle but it also has a locking mechanism with a hole that passes through the spindle at 90 degrees meaning it would not be air tight. I looked at the Hold Fast solution but it looked a bit of a faf to remove and I was on a very tight budget. I brew and had a load of 3/8 beer line and this fits through the spindle nicely. It can also be very quickly connected and disconnected with 'John Guest' fittings. These are absolutely superb fittings that work both under pressure and vacuum.
In my solution the rotary coupling is built into the chuck itself and the pipe is stationary in the spinning spindle. The pipe is tough but unlikely to damage the spindle and I have found this to be a robust solution in the 6 months I have been using it. It is worth checking the pipe every now and again as I am sure that one day it will wear through but a few pence and a replacement can be substituted. The rotary connection is a simple bearing pressed into the MDF. I drilled a hole with a forestner bit (I think an inch) and selected a slightly bigger OD bearing (26mm I think). The beer line simple press fits into the centre of the bearing. I was going to epoxy it in place but have not found this to be necessary.
I eventually found a pump on eBay for 30 pounds – think it was from somebody who posts in these forums as I saw a picture of the pump here in another post. In operation the pump pulls about 28 inches of mercury. Connected to my chuck it is 21 inches of mercury. I think most of the leak is through the bearing and if I did it again I would use either a double bearing or simply drill a deeper whole and push 2 bearings in there. I also only have a single coat of sealer on the MDF so that might also be an issue. Also the pump is on the weedy side. Anyway, 21 inches of mercury is not bad and the system has proved to be quite adequate in operation.
If anybody would like more details I can post some pics but going to Yandels now to buy some wood
I also have a couple of other projects that may be of interest. A home made air cleaner – Microcleneesque and an outboard turning attachment for my ancient Poolewood 28-40 lathe.
Cheers, BM.
I have been looking for an easier way to hold work to finish the bottom of bowls and the like. Don't particularly want to open the debate on whether this is necessary or not, just my personal preference. Anyway, I have used the tailstock method with a friction drive and this works OK with a couple of drawbacks: Access is difficult to the centre and only works for stuff that fits over my lathe bed (no use outboard). So I also used a ring (doughnut) chuck and got on well with it but it is a little scary with wing nuts flying around. This is still a solution I use occasional if my preferred solution, the vacuum chuck, isn't suitable.
I decided against Cole jaws and the Longworth chuck. I have heard mixed views on the longworth and the commercial cole jaws are not cheap and they are not suitable for natural edge. That left me with the idea of the vacuum chuck – nice but potentially very expensive.
Anyway, this is a short description of my vacuum chuck build. I have added it here because the design is slightly different to some of the others I have seen but with lots of blatant copying as well from folks like Bob Chapman (thanks Bob). Might give people some additional ideas. The overall cost was about 60 pounds – didn't keep a full bill of materials and has a few odds and sods to start with. I decided I wanted to use a proper vacuum pump, not a vacuum cleaner as this will give a better results on a small chuck. There is absolutely no reason a vacuum cleaner can't be made to work and indeed I did make up the chuck first and tried it with my wimpy shop vac and it worked – sort of. This was on a 4” chuck so I think would have been fine on a bigger chuck, say 8”.
The chuck is very similar to Bob's with an MDF base (must be sealed) and a soil pipe. For a gasket I use a lose disc of laminate floor underlay. The main difference to other solutions I have seen if the rotary adapter and pulling the vacuum through the spindle. My lathe has a hollow spindle but it also has a locking mechanism with a hole that passes through the spindle at 90 degrees meaning it would not be air tight. I looked at the Hold Fast solution but it looked a bit of a faf to remove and I was on a very tight budget. I brew and had a load of 3/8 beer line and this fits through the spindle nicely. It can also be very quickly connected and disconnected with 'John Guest' fittings. These are absolutely superb fittings that work both under pressure and vacuum.
In my solution the rotary coupling is built into the chuck itself and the pipe is stationary in the spinning spindle. The pipe is tough but unlikely to damage the spindle and I have found this to be a robust solution in the 6 months I have been using it. It is worth checking the pipe every now and again as I am sure that one day it will wear through but a few pence and a replacement can be substituted. The rotary connection is a simple bearing pressed into the MDF. I drilled a hole with a forestner bit (I think an inch) and selected a slightly bigger OD bearing (26mm I think). The beer line simple press fits into the centre of the bearing. I was going to epoxy it in place but have not found this to be necessary.
I eventually found a pump on eBay for 30 pounds – think it was from somebody who posts in these forums as I saw a picture of the pump here in another post. In operation the pump pulls about 28 inches of mercury. Connected to my chuck it is 21 inches of mercury. I think most of the leak is through the bearing and if I did it again I would use either a double bearing or simply drill a deeper whole and push 2 bearings in there. I also only have a single coat of sealer on the MDF so that might also be an issue. Also the pump is on the weedy side. Anyway, 21 inches of mercury is not bad and the system has proved to be quite adequate in operation.
If anybody would like more details I can post some pics but going to Yandels now to buy some wood
I also have a couple of other projects that may be of interest. A home made air cleaner – Microcleneesque and an outboard turning attachment for my ancient Poolewood 28-40 lathe.
Cheers, BM.
