Half Scale 1/4HP A J Weed Engine

[Jasonb]

To hold the part machined cylinder while the end flanges were given their "teardrop" shape I used the CNC to make a simple fixture with two spigots that located into the cylinder and valve bores and tapped for a couple of M6 fixings. It was then just a cas eof screwing the cylinder to the jig and running a 3D adaptive to remove the waste and then a finishing 2D contour on each end.



Any excuse for a quick test fit



I also turned up the cylinder and valve end covers. This is the spigot that will locate the cylinder into the trunk guide being turned as a second op and held in the softjaws and the trunk guide being used to gauge the final diameter





Here are the four covers with all the lathe work complete. I also turned the two bronze glands as "tophat" shapes and drilled their two stud holes in each.



Over to the CNC the holes were drilled and tapped as required, the bronze glands screwed into place and the two machined as one to their final elliptical profile.

Well it would be nice to say it all went well but I did make a bit of a booboo profiling the first cylinder end. I thought I would be clever and draw the jig in F360 with the larger spigot centred on the X-Y axis as that is what I had used as the datum on the cylinder CAM. However I forgot that when going from design to manufacture (CAM) in F360 the part centres on the material by default so when it came to cut the profile the cylinder was 10mm to the left of where the cutter thought it was. As you will see instead of taking a 0.6mm cut off the left edge the cutter went in at the full 6mm width. Luckily it was on the side of the teardrop where the most metal needed removing and I was able to click the stop icon before I cut into metal that was meant to remain, it also kicked the jig off to the right so that had to be centred up again.

<a href="https://www.youtube.com/watch?v=2gSx8cn384I" target="_blank">http://www.youtube.com/watch?v=2gSx8cn384I</a>

[Kim]

Yikes!  That must have given you a start!  Glad you were able to stop it quickly before it could do irreparable damage.  So kudos on an excellent recovery, Jason!  And the part ended up looking suburb, as always.

Kim

[Jasonb]

I have found that if something is going to go wrong then it is most likely right at the start so I have taken to holding the mouse over the stop icon straight after clicking start. I keep my finger hovering so can quickly stop the machine if needed.

Usual reasons are not setting the tool height or setting it but not entering it on the screen. I also don't have the spindle go up to a home position so can forget to remove the G28 from the file F360 produces, this one is quite easy to spot as the axis start moving before the spindle starts, but it can move quickly. Or as in this case getting the datum wrong so the machine cuts in the wrong position.

The image sbelow show how when sketched I had the XY datum centered on the bore, then how I also had the CAM for the cylinder centred on the bore and lastly how F360 defaulted to putting XY in the middle of the stock that the fixture was cut from

[Jasonb]

Swarf production continues at a pace. This time it is the flywheel which was cut from a 25mm slice of 95mm dia cast iron bar, infact m-Machine sent me 28mm so even more swarf! As I usually do I started on the lathe machining the OD, one side and boring to fit the crankshaft then flipped it over to face the other side.



Then over to the CNC to form the spokes. You are probably getting se dto this by now but an adaptive tool path was used to remove most of the waste material



Then a scallop path with a 4mm ball-ended cutter to finish it off. The two were repeated for the second side to complete the CNC work.



Those with a fear of getting cast iron swarf on their chucks and machines should look away now as this is what 40% of the bar now looks like with the remaining 60% as swarf. That wa sjust the CNC work, probably more like 25/75% if finished item compared with supplied stock.



After a quick bit of file work and a tickle with the Dremel to remove machining marks and give a bit of "casting" texture this is what the finished flywheel looks like. The engine I am basing mine on did not have the original flywheel so I have gone with something fairly chunky which seems to suit the rest of the engine which was made to do work rather than be looked at.



<a href="https://www.youtube.com/watch?v=T0Qm1bPoEZ0" target="_blank">http://www.youtube.com/watch?v=T0Qm1bPoEZ0</a>

[redhouseluv]

I like the sea of swarf you have created in miiling photo!

The finishing off you have done really does finish it off; really gives the appearance of a cast flywheel.......magic! 

[Casting Iron]

That is pretty interesting watching it carve out those tapered spokes.
Does a nice job.
.

[Krypto]

Thanks again for supplying these videos!  Very informative.

[Jasonb]

Thanks, it is a bit hard to know how much to include and how much to edit out and I certainly don't stand there videoing the whole lot but good to know it is of intereste.

Next up is the Conrod, on the original this is an iron casting and judging by the fracture may well have just been grey iron rather than ductile. I decided to cut it from Hot Rolled steel as there was little point in substituting a piece of Sg Iron bar. The first job was to bring the square bar that I had down to the maximum 16 x 11 which I did with an insert face mill flipping the bar over a few times to balance the cuts either side to help avoid distortion.



With the bar stood on end I drilled tapping size, then opene dup part way to 2.5mm before tapping th eremainder M2.5. The cap was then cut off, the sawn faces milled flat and a couple of temporary cap heads used to hold the cap in place while the holes wer reamed, the ends reduced in size and the fork milled





Over to the CNC it was screwed to a bit of scrap and one sid ethen the other machined with my Usual adaptive fillowed by scallop paths. There is a bit of air cutting at the small end as I did not bother to model the previous manual machining but just used a rectangular bar as the stock. I could also have rounded the end but at the Time of doing the CAM was going to use that for holding the work but in the end I screwed through the holes

<a href="https://www.youtube.com/watch?v=CuGtmCaUpX4" target="_blank">http://www.youtube.com/watch?v=CuGtmCaUpX4</a>

No pic of the finished rod but here you can see it being used as a clamp to make sure the soft solder holding the split bronze bearing together did not come apart during the drilling and reaming, just don't forget it is there as you can't really see it a a few 100rpm.

[redhouseluv]

That looks like a useful little 4-jaw you have inserted into the 3-jaw for small jobs. Is it a 80 or 100mm chuck with a straight shank backplate?

[Jasonb]

I'll need to go and measure it but approx 60mm. It is the one off my rarely used these days Emco Unimat3 which has a M14x1 threaded body. I bought a plain shank adaptor for it so can go in a collet or the jawed chucks. I use it more because I can't always be bothered to change chucks to the big 4-jaw than anything else.

[Jasonb]

The cylinder cladding sheet made a nice change from machining. I started by cutting a strip of 28g copper a couple of mm wider than the length of the cylinder and also about 10mm longer than needed as that was what size sheet I had. The first thing I did was to drill the clearance hole for the inlet boss by clamping to a suitably angled bit of wood to match the angle of the cylinder and then used a step drill to form the hole.



The strip was then wrapped around a couple of bits of bar to get the basic shape before screwing one end to the underside of the cylinders end flanges. I could then wrap it around the cylinder to mark the final length which was then cut and filed before adding another two screws to fix that end. With it screwed into place I filed off the extra length at each end until it was flush with the cylinder. When fitted the two ends butt up against each other but it needs a bit of spring to allow it to open and slide over the inlet boss.



The next item to tackle was the crosshead, like the original I made this from cast iron but used 25mm bar as my starting point rather than a casting. This was turned to just enter the trunk guide, faced and tapped M4 x 0.5 before being sawn off the bar and faced to final length. It was then lapped into the trunk guide with 600g silicon carbide powder mixed into a paste with oil.

Then over to the CNC for a bit of shaping. Adaptive with a 3mm tool to start, then the horizontal surfaces were finished with the same tool before changing to a 2mm dia ball nosed cutter to do the "hump". As this was fairly flat I opted for a parallel finish path with 0.15mm stepovers. Last thing that side was to drill and ream for the pin after which it was turned over so the same milling paths could be run again to do the other side.



<a href="https://www.youtube.com/watch?v=Dk947mkAEl4" target="_blank">http://www.youtube.com/watch?v=Dk947mkAEl4</a>

[Jasonb]

Like the crosshead the eccentric strap on the original was an iron casting so I also cut mine from the same material. Starting with a slice off the end of a suitable block that was machined to the overall width and thickness, then cut in two and the sawn edges machined. I then tapped two holes in the larger half and drilled two clearance size holes in the other, after which they were screwed together and bored to the size of a suitably sized plug.



So that I could get in better with the milling cutters for the following ops I milled away the waste to leave the lugs either side. And also tapped the hole for the eccentric rod.



Suitably clamped to a bit of bar so that it could be held securely it was over to the CNC to continue the machining. My usual methods of an adaptive toolpath to start this time with a 2.5mm dia cutter and then a scallop with a 3mm ball nosed one.



Back to the manual mill and the other side was rounded, some corners knocked off with needle files and that completed the eccentric. The clevis and fork are fairly straightforward forward machining as was bending the eccentric rod.



<a href="https://www.youtube.com/watch?v=_mROSr1DZu4" target="_blank">http://www.youtube.com/watch?v=_mROSr1DZu4</a>

That just about wrapped up the parts except for a couple of pivot pins and just over 40 assorted fillister headed screws in M1.6, M2.5 an dM3 as the video of te horiginal mentioned that the whole engine could be stripped with just a screwdriver.

[redhouseluv]

The clevis and fork are fairly straightforward forward machining as was bending the eccentric rod.

The strap, sheave, rod and fork look great

I have to do some eccentric rod bending on my build, what is the technique, where do you know where to bend and how do you work out the angle of each bit ........

[Jasonb]

I did not really do anything special, just bent it.

When I drew up the engine a did it so the angled part of the rod was approx parallel to the sloping side of the base although it is actually a lazy "S" shape not a straight edge. So that gave me the angle I needed to bend to so I just offered the rod upto the side of the engine base to gauge the bend, I could have printed it out and used that as a template which I do for more complex or critical bending.

The central section fitted nicely in my small 35mm vice so the overlength piece of 2.5mm rod was held in that and an adjustable spanner used to bend each end. If you make sure the spanner is the same distance from the edge of the vice for both bends then you will get a similar bend radius and what is in the spanner and beyond will stay straight. Looking down the newly bent rod will show if the two ends are parallel or not.

The eccentric end was then cut to length and threaded so it could be screwed into the starp and the amount of offset checked, a quick tweak or two until the rod naturally falls inline with the valve rod then you know it won't be making teh strap rub on the side of the eccentric.

[redhouseluv]

Thanks, so from what you have said its very much a 'by eye' method, but using a spanner and vice and checking is the sections are pararllel. The length I have is quite stubby and short and so will need to be practised on a piece of scrap first