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Converting my old pneumatic retracts to electric.
- Thread starter Flyinfool
- Start date
- Joined
- Apr 29, 2019
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- 2,059
OK here is the preliminary drawing for the Trunion.
I have to look closer. I may be able to repair and/or compensate for the worn material.
The worn area is the .437 bore. I have a wrap of .002 shim stock around the part that goes into that hole. the slot and screw are to make a clamp out of the trunion.
More pondering...........
I have to look closer. I may be able to repair and/or compensate for the worn material.
The worn area is the .437 bore. I have a wrap of .002 shim stock around the part that goes into that hole. the slot and screw are to make a clamp out of the trunion.
More pondering...........
- Joined
- Apr 29, 2019
- Messages
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I have never had a set of Spring Air, but have seen them on other planes at the field.
Last edited:
- Joined
- Apr 29, 2019
- Messages
- 2,059
I did set up one of the existing trunions and made a small modification to it and just from how the cutter worked it is definitely not 7075 like I am using for all of my parts as it machined as a more gummy feeling and is much softer alloy.
Soooo....... I am at least going to attempt to make the trunions from scratch.
This way I know they are out of a stronger alloy and will stand a much better chance of a long happy life that cutting a deep slot across the existing and softer trunions.
They will be tricky and I will need to acquire some new skills, knowledge and tools.
I did make another post in a more general area for ideas on how to cut one of the features as my poor little brain was just not seeing it. I have made some changes since the version posted back in post #52
www.hobby-machinist.com
So far I have only worked on getting the drawings complete, and ordered some of the new tooling that will be needed and some of the material to make other tools that will be needed.
I am still in the process of designing a holding fixture that will go onto the rotary table. This will allow me to do almost all of the machining in the one fixture. I also need to calculate out all of the tool offsets with the X,Y locations of each cuts start and stop points since the location of edges will move as the table is rotated.
Here is a preliminary drawing of the part, this is only sheet one of five so it may be a bit hard to see everything. Each sheet has specific details for each cut so as to avoid using a wrong dimensions while spinning the part around.
The initial plan is to start by lopping off a 2 inch chunk of my 30mm round bar of 7075.
I did plan far enough ahead that the bar is JUST big enough to get this part out of.
I have already machined that chunk into a nice rectangle that is oversize in all dimensions except the 0.620 thickness that is the one dimension that I machined to size.
the plan of operations at this point in time. Some of this is just thinking out loud and is very subject to change,
1. Drill and ream the 3/16 pivot hole to be able to use that as a locating point for all other operations. The fixture will have a 3/16 pull out dowel pin in it. the pull out dowel is taped 8/32 on both ends so it can be pressed and screwed into the fixture and another screw can clamp the part in position.
2. There is another thru hole that is drilled, tapped, and c'bored for a 6/32 screw that clamps the strut of the landing gear in place. I will drill this hole undersized with a very tight fit to a smaller screw Probably a M3 or a #4-40 screw. This will be the second clamping point to prevent the part rotating while cutting, I will then later drill, tap and c'bore to final size after all other machining is done. This mounting to the fixture plate will allow full access to all side of the part for machining to final size and shape.
Now comes the fun
3. Machine the top edge and then rotate the table to machine the 1.000 radius and then continue down that edge off the part to get that angle.
4. With the table still at this angle machine the parallel edge to the precalculated stop point for that edge, lift the cutter rotate the table back to zero, this will allow me to machine the bottom edge and the left end to final sizes. All of this will be done with a 1/2 inch cutter to leave the .250 inside radius in the bottom inside corner. Finally rotate the table to make the .719R on the right side of the part.
5. One more table turn to get that small angle cut on the bottom left corner.
6. With the outside profile now complete and to size (I hope), I will use a slotting saw to make the .204 wide slot at the 78.75° angle.
7. Remove the M3 clamp screw and do the final drill, tap, and c'bore of the clamp screw hole.
8. Now moving to the Vice. Set the part on end to make the 0.437 bore.
9. Flip the part to have the top up, I can make the .156 wide slot to depth. then make the .093 wide slot to turn the .437 bore into a clamp.
10. Another part flip to make the .259 wide slot with an end mill.
I am thinking that I will again do both parts at the same time so each setup only needs to be done once.
OK this was long, a lot of thinking out loud on my part.
As always I am wide open to thoughts and other ideas that I may not have thought of.
Soooo....... I am at least going to attempt to make the trunions from scratch.
This way I know they are out of a stronger alloy and will stand a much better chance of a long happy life that cutting a deep slot across the existing and softer trunions.
They will be tricky and I will need to acquire some new skills, knowledge and tools.
I did make another post in a more general area for ideas on how to cut one of the features as my poor little brain was just not seeing it. I have made some changes since the version posted back in post #52
Cutting a slot at a weird angle and size.
Project I am working on requires a slot be cut in the side of the part at a 78.75° angle to the center line. The slot needs to be .204 wide and .437 deep. Of course there is no surface square or even an even degree from this slot to set up on. The part will already be on the rotary table for...
www.hobby-machinist.com
So far I have only worked on getting the drawings complete, and ordered some of the new tooling that will be needed and some of the material to make other tools that will be needed.
I am still in the process of designing a holding fixture that will go onto the rotary table. This will allow me to do almost all of the machining in the one fixture. I also need to calculate out all of the tool offsets with the X,Y locations of each cuts start and stop points since the location of edges will move as the table is rotated.
Here is a preliminary drawing of the part, this is only sheet one of five so it may be a bit hard to see everything. Each sheet has specific details for each cut so as to avoid using a wrong dimensions while spinning the part around.
The initial plan is to start by lopping off a 2 inch chunk of my 30mm round bar of 7075.
I did plan far enough ahead that the bar is JUST big enough to get this part out of.
I have already machined that chunk into a nice rectangle that is oversize in all dimensions except the 0.620 thickness that is the one dimension that I machined to size.
the plan of operations at this point in time. Some of this is just thinking out loud and is very subject to change,
1. Drill and ream the 3/16 pivot hole to be able to use that as a locating point for all other operations. The fixture will have a 3/16 pull out dowel pin in it. the pull out dowel is taped 8/32 on both ends so it can be pressed and screwed into the fixture and another screw can clamp the part in position.
2. There is another thru hole that is drilled, tapped, and c'bored for a 6/32 screw that clamps the strut of the landing gear in place. I will drill this hole undersized with a very tight fit to a smaller screw Probably a M3 or a #4-40 screw. This will be the second clamping point to prevent the part rotating while cutting, I will then later drill, tap and c'bore to final size after all other machining is done. This mounting to the fixture plate will allow full access to all side of the part for machining to final size and shape.
Now comes the fun
3. Machine the top edge and then rotate the table to machine the 1.000 radius and then continue down that edge off the part to get that angle.
4. With the table still at this angle machine the parallel edge to the precalculated stop point for that edge, lift the cutter rotate the table back to zero, this will allow me to machine the bottom edge and the left end to final sizes. All of this will be done with a 1/2 inch cutter to leave the .250 inside radius in the bottom inside corner. Finally rotate the table to make the .719R on the right side of the part.
5. One more table turn to get that small angle cut on the bottom left corner.
6. With the outside profile now complete and to size (I hope), I will use a slotting saw to make the .204 wide slot at the 78.75° angle.
7. Remove the M3 clamp screw and do the final drill, tap, and c'bore of the clamp screw hole.
8. Now moving to the Vice. Set the part on end to make the 0.437 bore.
9. Flip the part to have the top up, I can make the .156 wide slot to depth. then make the .093 wide slot to turn the .437 bore into a clamp.
10. Another part flip to make the .259 wide slot with an end mill.
I am thinking that I will again do both parts at the same time so each setup only needs to be done once.
OK this was long, a lot of thinking out loud on my part.
As always I am wide open to thoughts and other ideas that I may not have thought of.
Just read through the thread. I’ve been flying models since I was a kid in the ‘60s and RC since 1978. Just wanted to pass along my admiration for the work you’re doing here. When I was working on 1911 pistols a lot I kept 1/16” center cutting end mills on hand. They would cut through stubborn roll pins like they were aluminum.
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- Jul 29, 2014
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- 2,737
I wish any of my RC planes would have been around long enough to wear out. 
I wish any of my RC planes would have been around long enough to wear out.
Mine last longer due to not flying a lot……………
- Joined
- Apr 29, 2019
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- 2,059
This near 20 year old jet is one of my younger big aircraft.
I have several over 30 YO.
It was quite a few years back that I decided to just not crash any more. I have no need to flirt with any large planets to try to impress people.
Not that I crash any less either.........
I have several over 30 YO.
It was quite a few years back that I decided to just not crash any more. I have no need to flirt with any large planets to try to impress people.
Not that I crash any less either.........
- Joined
- Apr 29, 2019
- Messages
- 2,059
Making some progress.
Got the main fixture to hold the part on the rotary table done. It is not much to look at. On the rt it is just a 4" round disc with 4 tiny M3 tapped holes for mounting the trunion blank. The little holes do not even show up much in a pic.
The pull out dowel pin is not what I thought, they only come tapped on one end, not both. I assume that dowel pins are to hard to tap.
So I am next making a pin that will be tapped on both ends, then I will be ready to start chopping off metal on the actual trunions.
Got the main fixture to hold the part on the rotary table done. It is not much to look at. On the rt it is just a 4" round disc with 4 tiny M3 tapped holes for mounting the trunion blank. The little holes do not even show up much in a pic.
The pull out dowel pin is not what I thought, they only come tapped on one end, not both. I assume that dowel pins are to hard to tap.
So I am next making a pin that will be tapped on both ends, then I will be ready to start chopping off metal on the actual trunions.
- Joined
- Apr 29, 2019
- Messages
- 2,059
Aaarrrrggggg......
Was close to ready to start making chips on the trunions.
My poor RPC that powers the 3PH parts of my shop started to make an awful bearing type noise. Still putting out proper power, just got real loud real fastI thought they would last much longer than this one did. It has only been powering my shop for the last 32 years.
Soooooo now my next job is to dig out the RPC and disassemble to see if it can be fixed or if it must be replaced.
Was close to ready to start making chips on the trunions.
My poor RPC that powers the 3PH parts of my shop started to make an awful bearing type noise. Still putting out proper power, just got real loud real fastI thought they would last much longer than this one did. It has only been powering my shop for the last 32 years.
Soooooo now my next job is to dig out the RPC and disassemble to see if it can be fixed or if it must be replaced.