Model Engine Maker
Help! => Specific Engine Help => Topic started by: Heffalump on February 25, 2014, 09:30:22 AM
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Hiya chaps,
I'm building Elmer's 33, and have come to the radiused slot in the base. I saw stan did this with a tool I do not have! What options are there for cutting this slot?
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Take a piece of 1/2" diameter drill rod, grind the end to the half width line and profile it to give some clearance at the back. Harden it. Then use it as a flycutter, sticking sideways out of a "boring" bar at the appropriate diameter.
Your cutter will have one tooth, Stan's had many more so take it very slowly and steadily as you cut.
Jo
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One other thing we are lacking is a boring tool for the mill!
Aside from not looking as pretty, would this feature function as well with a flat bottom instead of a radius?
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It shouldn't affect the function at all...just a matter of aesthetics. Looking at the plans, the slot is for clearance of the crank disk and con rod. The flat bottom will show but the engine will still run fine. It looks like the side to side clearance (or width of the slot) is far more critical.
Bill
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Just wondering out loud here - if I'm being stupid, just ignore...
Assuming the base is aluminum...
A (woodworking) dado head
or
a small carbide-tipped 2.5" saw blade - the type used on small panel saws.
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That would work Marv, even a non carbide slitting saw would do, it would just take repeated cuts until the width was achieved, and a little more clean up at the end. The 2 1/2 diameter doesn't appear to be critical so even a 2" saw or 3" one should work if available...the wider the better of course.
Bill
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That would work Marv, even a non carbide slitting saw would do, it would just take repeated cuts until the width was achieved, and a little more clean up at the end. The 2 1/2 diameter doesn't appear to be critical so even a 2" saw or 3" one should work if available...the wider the better of course.
The flywheel is 3" diameter so I don't understand why the radius is less than half that (1.5"). Esthetically, I would expect it to be larger.
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One other thing we are lacking is a boring tool for the mill!
Aside from not looking as pretty, would this feature function as well with a flat bottom instead of a radius?
I used a flat bottom, then angled the piece and cut a ramp. It doesn't look too bad that way.
Alan
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One other thing we are lacking is a boring tool for the mill!
Aside from not looking as pretty, would this feature function as well with a flat bottom instead of a radius?
I used a flat bottom, then angled the piece and cut a ramp. It doesn't look too bad that way.
Alan
Ah that's quite a nice halfway house, I might do that as the cheapest option. The nodding / tilting head on the Bridgeport will make that easy.
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Marv, the flywheel on this engine sits outside the "base." The radiused slot is for the crank disk and connecting rod. Even so, it is more than generous at 2.5" diameter.
Bill
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Make the base from 3 pieces fastened together.
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Hiya Chaps,
I've annotated the drawing attached below, are these holes meant to be tapped?
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Jim
No tapping there. Those are clearance holes for the screws that affix the cylinder.(which is tapped). The side view shows them as countersunk for flathead screws. I used SHCS, so mine are counterbored.
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Would you like me to put all of these little query threads together into a single "Questions about the Elmer 33" thread?
Jo
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Yes please Jo! I am likely going to have many more - That's a much better idea.
Thanks Stan, does the #4-40 just refer to a drill size? I'm pants with imperial!
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4-40 is an american thread size. As you are in the UK it is probably better you look to make all your threads either BA or Metric (depending on what taps/dies you have).
I find that this is a useful chart for converting between thread sizes: http://www.metricmcc.com/catalog/ch10/10-1012.pdf
Jo
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So on the drawing here It lists a thread size, but I should be drilling not tapping?
:help:
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Those are clearance, the holes they line up on the other part are tapping size. (Assuming you don't have DROs) I would start by drilling the tapping size then later use the base to drill through into the parts they attach to.
When you get that far ask how to accurately align the two parts, there is a simple trick to do with drilling and tapping for one mounting screw and then putting the screw in and using that to secure for drilling the second one. Only after then do you finally open up the base holes to clearance size ;)
Jo
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Ah OK, so it's telling me to drill a hole big enough to allow for the #4-40 screw that will be passing through. That makes more sense.
I'm lucky enough to have a nice big DRO on the bridgeport, so I'm being as accurate as I can and hoping everything lines up afterwards, or is that a bit too hopeful?
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Hi Jim
The two countersink screws should be drilled for clearance for #4-40, and the hole showing between them should be drilled and tapped for #6-32 thread.
Don't drill the hole between them through into the groove either - it should be a blind hole. Basically, looking at the base, all the blind holes from the top must be threaded for #3-48, the three blind holes from the bottom must be threaded #6-32, and all the through-holes should be drilled at clearance size for #4-40.
M3 metric screws are a great replacement for the #4-40 American threads on most parts of Elmer's engines. If you do use different fasteners than the American ones specified, make a note on your plans to that effect next to mating parts - so that you can keep track of which holes must be what sizes.
Kind regards, Arnold
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Hi Jim
The two countersink screws should be drilled for clearance for #4-40, and the hole showing between them should be drilled and tapped for #6-32 thread.
Don't drill the hole between them through into the groove either - it should be a blind hole. Basically, looking at the base, all the blind holes from the top must be threaded for #3-48, the three blind holes from the bottom must be threaded #6-32, and all the through-holes should be drilled at clearance size for #4-40.
M3 metric screws are a great replacement for the #4-40 American threads on most parts of Elmer's engines. If you do use different fasteners than the American ones specified, make a note on your plans to that effect next to mating parts - so that you can keep track of which holes must be what sizes.
Kind regards, Arnold
That's grand, thank you.
I have replaced #4-40 with M3, and the #6-32 although they should be M3.5 I have the hardware for M3 and scaled them down, whether this comes back to bite me I do not know! Good point about annotating the drawing - I know too well the dangers of head knowledge ha! :)
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Hiya - I'm struggling a little with my visualisation. I'm going through my drawing and converting to metric sizes as I go, and I'm looking at the con-rod. I've rounded down the measurement indicated below to 4mm, but I can't work out what actually fits in that hole. I think this must be the crank pin? Just looking for confirmation really, as on my plans the very right hand side of the page has been clipped and some information is missing.
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Yes it is the crank pin.
I would look to go up to 5mm rather than down to 4mm. If you are worried about the amount of metal left either side of the pin you could reduce the diameter of the curve on the top and bottom (hand file rather than turn).
Jo
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Yes it is the crank pin.
I would look to go up to 5mm rather than down to 4mm. If you are worried about the amount of metal left either side of the pin you could reduce the diameter of the curve on the top and bottom (hand file rather than turn).
Jo
ED just realised I said 4mm but I meant 4.5mm
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Jim
Print this chart. Keep it handy. I use mine (Imperial) all the time.
https://littlemachineshop.com/Reference/TapDrillSizes.pdf
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What's the best way to cut out a chunk of aluminium from a larger billet? Our bandsaw is too weedy. Is it time for more hacksawing?
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Reciprocating saw (Sawzall)
Oxy cutting torch
Angle grinder
Chain drilling/hacksawing
Water jet :Lol:
Plasma cutter :ROFL:
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Bigger band saw would help :mischief:
Or get some smaller stock
Sorry only joking
Stuart
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use your weedy band saw cut part the way turn the material cut part the turn again and you can get through the worst if not all the way if you have no cutting fluid rub some ordinary hand soap (bar of)on the teeth also good when filling aluminium stops it clogging. ian c
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Thanks Chaps.
If I want to run this engine on steam, what is the best material for the cylinder? I know that Ali is a good choice for running on air, easy to machine, cheapish, but will it stand up to a battering from steam?
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Running on steam
well two choices
one bronze with a different grade bronze piston and soft packing ( i mean say cast for one and drawn for the other bit ) this combo is good if you do not run often no rust
two Cast Iron cylinder and cast iron piston with CI rings or soft packing will rust up if not used often
note in both cases you will need a lubricator in the steam line displacement type will be ok ( note this will not work when run on air) a mechanical one will do both air and steam
I have seen loco's that have bronze cylinders and cast ali piston ( but the ali was not degassed and was left full of bass inclusions to hold the oil , soft packing in this case )
note if you are using super heated steam at 100 psi then only CI is good enough the temp would be a bit high for a bronze set up , but it would work but not as good as CI
IMHO use CI and CI rings and do the job properly
Have fun
Stuart
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Thanks Stuart. I think I'm probably looking around 30-40 PSI max for simple steam.
Why is Ali no good?
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Unless you can dry it out it will corrida with the white deposit you will have seen
Also it will expand with the heat and produce a poor fit for the piston
BTW when I say soft packing it's graphited yarn , I do not like silicon o rings as piston rings ,because unless you can hone the cylinder to a mirror finish and produce the grove to the o ring data tables for the use that you are doing it will not work long term
Soft packing has been used for years , as have CI rings ,but you will need to heat react them to get the spring correct
But I am sure others will chip in and give you a different opinion but my advice is based on my experience over 40 years
Stuart