Building a Feeney 4 Cycle, crankcases came out fine, cylinder liner also good. Started boring the cylinder casting & found it off square (see photos). Issue now is to get a good set-up. It's at 1.050" going to 1.250" so I have room enough to work with, but am going nuts trying to get it in the 4 jaw any way near close. Thinking of building some kind of jig, but thought first I'd ask for ideas, seems I get tunnel vision when I get stuck, and can't see the obvious right in front of me
Bored off square - How to fix?
- Thread starter Rod Cole
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Help Support Home Model Engine Machinist Forum:
Dave, this is a new project not a repair. I stopped at 1.050" with .200 to go, it may have cleaned up the way it was, but I knew the one valve would be awfully close the the cylinder wall - just not right!
You use 4 jaw chuck or set on mill.
The mill is easier than lathe.
You can start mill and finish in lathe.
If it to far just use DOM tubing as sleeve
FYI
If it old engine sometime manufacturers would do funny things to fix a error. So trying may not best thing
rklopp
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I would not try to hold that casting directly in a 4-jaw chuck. Try grabbing the flange along the lines shown in the photo below, holding the cylinder to a fixture block or plate, then grabbing the block in your 4-jaw or mill vise. Since there are no holes in your flange, you'll need some pinch clamps instead. In the case of the operation shown in the photo, the cylinder flange had been cleaned up previously by holding the rough cylinder bore on an expanding mandrel and facing the flange in the lathe. You may have a challenge with an expanding mandrel since your bore is cockeyed, but you can get creative with tilting and offsetting the mandrel in a 4-jaw with shims. It often pays to spend significant time making fixtures to hold a tricky part in order to avoid a screwup. Ron Chernich's old site offers some great ideas for solving the issue. Surf to https://modelenginenews.org/ and then Projects > Morton M5.
I like the looks of that set-up, and will look up that link you supplied. The best I could think of was something like what they call a "spider" that you put on the far end of a lathe spindle to hold long stock from becoming a helicopter. I didn't like the spider idea for fear of the screw points doing damage or else not being secure enough.
The set up you have in the photo looks just fine to me, and easy to adjust to perfection. I guess my biggest issue is to get past not wanting to build jigs. When I see plans calling for some form of jig the first thing I do is try to get around it. Time to stop that.
rklopp
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Indeed. My collection of various single-use jigs and fixtures is at least as big as my collection of finished engines. It took years for me to learn that general workholding devices, like lathe jaw chucks and mill vises, can be sketchy at holding castings.
Rod,
I understand your concerns. I am working on an old casting kit with similar issues. Have you considered using "Cerrobend" type low melt alloy to encapsulate the cylinder in a square aluminum "tank" which would be held in the mill using an expandable arbor positioning it vertically prior to pouring. The container would be dimensionally accurate to permit machining operations from the mill to the 4 jaw in the lathe. I have had excellent results and also have reused the pour tank for other 4 stroke ICE model engine builds less than 1.5" bore. The alloy is also saved. I always test the cylinder metal with the low temp alloy to be sure it does not affect the cosmetics when melted and removed. If you use this, be sure to do it outdoors and not exceed the melting temp by too much to prevent outgassing vapors.
Thanks for you post!
Good luck,
Wes
Wes:
A most amazing idea, I've already started to make up something like "rklopp" has shown me above however this is one I'll keep in mind for the future!! This is what this forum is all about - a place you can find competent ideas from people who want to help others. Thank you Wes.
A most amazing idea, I've already started to make up something like "rklopp" has shown me above however this is one I'll keep in mind for the future!! This is what this forum is all about - a place you can find competent ideas from people who want to help others. Thank you Wes.
Rod,
To machine a casting you have to think like a casting. Bad joke, I know, but only partly in jest. That is a fairly complex casting and as you said getting it set up correctly is critical.
Look at the parting lines on the casting. The main outside shape with the fins has a single main parting line made from the 2 halves of the mold. The inside of the flanged ports on either side probably had separate cores. The cylinder bore also had a separate long core that included the valve pockets, and that core was only supported at one end. As you bored deeper and deeper it got worse and worse. So, the main outside finned halves (which you want to be centered to look nice in the finished model) go together well, but any or all of the cores could be misaligned and not clean-up evenly. That can be typical of some castings.
Here is a way that is time consuming but is accurate, and you generally don't have make much of a machining fixture.
Start by painting all the surfaces that will be machined with machinists blue. Now you need to scribe some lines. You could ( and probably should) start by turning a piece of wood to fit into the bore of the casting. Secure that piece of wood securely, vertically, onto a nice flat surface and set the casting on it. It is best if it fits slightly snug, not sloppy. Now, referencing off the flat surface that wooden post is attached to, check some squarnesses, and things like the flange faces, and the levelness of the fins. Most likely you will find that if the core is vertical, those other features will be tilted. If that is the case, tilt and re-secure the center wooden post to bring the external features into their correct planes, if possible. You said there is a lot of spare metal in the bore, so see how true you can get the outside features without tilting everything too-too much.
Now that the casting is positioned better, touch the blueing up and again scribe some lines where the external machining cuts will be. Once you like how the casting is sitting, you will have to pick some datum surfaces to work from. This is where you can avoid the fixtures. Think how you might position this casting on the mill to take just a few preliminary cuts. Not finish cuts, but instead you will add an equal amount of stock to those 3 or 4 cuts.
So now with the casting still on the wooden post, take an angle grinder and LIGHTLY remove a little material from maybe 3 or 4 small areas to make small surfaces to rest on when you put the part on the mill. If you grind those 3 spots accurately according to your scribe lines and then set it on those points on your mill and clamp it into place on the table, THEN you can take those prelim mill cuts to establish your datum surfaces.
I know this sounds like a PITA, and it definitely is, with all marking and scribing and adjusting and marking again. Castings are seldom very accurate (unless they are investment or other precision casting process) and you want to catch your mistakes with the layout blue, not after you have machined the metal off.
When you are machining those prelim datum cuts you can also machine a few places to clamp on with your 4-jaw, so that you can proceed with some confidence that you know where the finished surfaces will end up.
I know this is long, but it does work.
Lloyd
To machine a casting you have to think like a casting. Bad joke, I know, but only partly in jest. That is a fairly complex casting and as you said getting it set up correctly is critical.
Look at the parting lines on the casting. The main outside shape with the fins has a single main parting line made from the 2 halves of the mold. The inside of the flanged ports on either side probably had separate cores. The cylinder bore also had a separate long core that included the valve pockets, and that core was only supported at one end. As you bored deeper and deeper it got worse and worse. So, the main outside finned halves (which you want to be centered to look nice in the finished model) go together well, but any or all of the cores could be misaligned and not clean-up evenly. That can be typical of some castings.
Here is a way that is time consuming but is accurate, and you generally don't have make much of a machining fixture.
Start by painting all the surfaces that will be machined with machinists blue. Now you need to scribe some lines. You could ( and probably should) start by turning a piece of wood to fit into the bore of the casting. Secure that piece of wood securely, vertically, onto a nice flat surface and set the casting on it. It is best if it fits slightly snug, not sloppy. Now, referencing off the flat surface that wooden post is attached to, check some squarnesses, and things like the flange faces, and the levelness of the fins. Most likely you will find that if the core is vertical, those other features will be tilted. If that is the case, tilt and re-secure the center wooden post to bring the external features into their correct planes, if possible. You said there is a lot of spare metal in the bore, so see how true you can get the outside features without tilting everything too-too much.
Now that the casting is positioned better, touch the blueing up and again scribe some lines where the external machining cuts will be. Once you like how the casting is sitting, you will have to pick some datum surfaces to work from. This is where you can avoid the fixtures. Think how you might position this casting on the mill to take just a few preliminary cuts. Not finish cuts, but instead you will add an equal amount of stock to those 3 or 4 cuts.
So now with the casting still on the wooden post, take an angle grinder and LIGHTLY remove a little material from maybe 3 or 4 small areas to make small surfaces to rest on when you put the part on the mill. If you grind those 3 spots accurately according to your scribe lines and then set it on those points on your mill and clamp it into place on the table, THEN you can take those prelim mill cuts to establish your datum surfaces.
I know this sounds like a PITA, and it definitely is, with all marking and scribing and adjusting and marking again. Castings are seldom very accurate (unless they are investment or other precision casting process) and you want to catch your mistakes with the layout blue, not after you have machined the metal off.
When you are machining those prelim datum cuts you can also machine a few places to clamp on with your 4-jaw, so that you can proceed with some confidence that you know where the finished surfaces will end up.
I know this is long, but it does work.
Lloyd
I like this idea, clearly logical and will make the end product look right. However, like you say it may be a PITA, but then if the job is to come out right - who said it would be easy
Where I worked for many years we used lots and lots of castings made by different vendors by different processes. Sometimes it wasn't until the 3rd or 4th order, after feedback to the vendor about how the casting needed to be adjusted, and after adjustments to our fixturing, that we got castings that could consistently be secured in the first operation fixture, and the machining would come out correct all the way to the final op. And after you started getting good castings from a vendor, you would NEVER change to a different vendor.
If you ever go to a casting house and see the number of different steps that it takes to make a casting, and the opportunities there are for tolerance buildup and inaccuracies, you will be a bit surprised at just how good the castings are, LOL. Castings can save a lot of time in the long-run, but its not like chucking a piece of bar stock in the lathe. Sorry if this sounds like a lecture, I just have lots of memories about the subject, ha ha.
The only foundry I've ever been in, was when I worked at Polich-Tallix. We had a plumbing & heating business and got a lot of work there. We ran gas lines, big steam lines, hooked up a cooling tower from the water cooled melting pots to the outside cooler, etc. I loved watching them build the sand casting moulds, like 6 foot square or bigger on the floor and then fill it with stainless. Also saw some cool lost wax work. Just endless stories about that place, I was so fascinated with their work I don't know how I got my own work done~ Look them up, amazing art work
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If you use resin-bound sand correctly, you can get some very round castings, like cylinders and flywheels, and you can see that they are round because you can chuck them up, and they run square inside and out.
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Just read this thread. I won't offer my ideas, as Wes and Lloyd have done so already, and very much better than I could!
I have never used Cerrobend alloy, but have heard of lead or tin or tin-lead solder being used (blacken the casting - smoke, pencil wax or graphite - so it doesn't "tin"). I have filled copper tubes with solder and wax for bending - to prevent collapse. Wax easier to use, but solder gave better bends.
Must get some Cerrobend.
But I have used wood. And candle wax (not for machining, but for holding parts for marking-out). You can warm wax inside your clothes (use body heat), and work it by hand until it is malleable then stick the part on it on a surface plate. It should hold while you mark it out.
K2
I have never used Cerrobend alloy, but have heard of lead or tin or tin-lead solder being used (blacken the casting - smoke, pencil wax or graphite - so it doesn't "tin"). I have filled copper tubes with solder and wax for bending - to prevent collapse. Wax easier to use, but solder gave better bends.
Must get some Cerrobend.
But I have used wood. And candle wax (not for machining, but for holding parts for marking-out). You can warm wax inside your clothes (use body heat), and work it by hand until it is malleable then stick the part on it on a surface plate. It should hold while you mark it out.
K2
Agreed! There was one large complex spherical shaped gimbal frame that we bought for over 20 years from the same vendor. About 5 years into the deliveries they switched from green sand to resin bound. WOW, what a difference in the dimensional consistency and accuracy!
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I like that wax idea for temporary leveling. I have used a hot glue gun, too.
Here is a link to Roto metals who is a big seller in the US of all sorts of light weight and low temp and babbit alloys. I don't know if they have any distribution in the UK.
https://www.rotometals.com/roto203f-low-melt-fusible-bismuth-based-lead-tin-alloy-ingot/
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Aha! Hot Melt glue! - Didn't think of that one! I love all the ideas that appear here..
I use lead as my "low temperature" melt metal. Because I have a lot... And carbon blacking - from a candle or oil lamp - makes a good surface prep to prevent the lead from tinning the surface. BUT the job needs to be stable when re-heated afterwards to melt the lead out at around 200C.
K2
I use lead as my "low temperature" melt metal. Because I have a lot... And carbon blacking - from a candle or oil lamp - makes a good surface prep to prevent the lead from tinning the surface. BUT the job needs to be stable when re-heated afterwards to melt the lead out at around 200C.
K2
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