Half Scale 1/4HP A J Weed Engine

[JasonBModerator @jasonb]

And so begins another engine build. This time the subject is a 1/4HP A J Weed steam engine as featured in the 1895 Chas A Strelinger & Co catalogue which was the second smallest in a range of casting sets for workshop engines they sold range from 1/8HP to 2HP. This is also said to be the same engine that P M Research based their #6CI on, I have not seen the PMR drawings but have based my half size version on some Youtube videos of an engine restoration and the list of various sizes of parts given as part of the spec in the Strelinger catalogue.

A true half scale would be 3/4″ bore x 1.25″ stroke but my metric version is actually 20mm bore x 31mm stroke, 90mm flywheel and comes out at 210mm long.

There will be quite a lot of CNC work on this one so look away now if that is not your thing. I also gave 3D metal printing a go for one part, more of that later.

Aluminium worked out the best option for making the bed “casting” so a block was reduced in size to leave 1mm all round the sides and then the bottom had 1mm skimmed off with an 809mm facemill after which I tapped two M6 holes so a block of metal could be screwed on and that in turn held in the vice.

The first job on the CNC was just to use the jog as a power feed and skim 1mm off the top with a 25mm insert cutter bringing the 1.25″ stock down to the required 30mm height.

It was then just a case of running the various paths, first was an adaptive to remove most of the waste, then a scallop that finished all the main surfaces – the vertical ones all have 2degrees of draft angle to mimic a casting. Then a quick horizontal for the tops of the feet and finally spot drilling and then drilling the tapping size holes for the bearing blocks and trunk guide. The holes were tapped M2.5 and M3 using the tapping function of the SX2.7mill to start the blind holes with spiral flute taps then finished to final depth by hand. A quick rub over with Emery to remove the cosmetic tool marks and the base was done.

More details of feeds and speeds in the video.

[DiogenesParticipant @diogenes]

Why the kind of ramping up and down the sides at the head end @ 2 mins in?..

[Adrian R2Participant @adrianr2]

Looks more aerospace than Victorian. With what you now know about 3D metal printing, could this base have been economically produced in a batch with the slide, and possibly other parts?

[JasonBModerator @jasonb]

The 3D Scallop finish path takes some weird and wonderful routes. Basically it steps over a given amount which in this case was set at 0.2mm no matter what the angle of the surface is. So unlike the Adaptive which leaves horizontal steps much like contours on a map the scallop can end up moving in quite complex paths as it may reach a more vertical edge in one direction while still cutting a near horizontal area in the other. I expect the software works out the shortest route to cover the whole surface and that is why it can seem quite random at times.

 

[JasonBModerator @jasonb]

Adrian, I’ll get some prices for various options and post the results in the other thread, probably won’t be until later today. Should also be able to work out what it would cost me to have cast in the UK.

[DiogenesParticipant @diogenes]

..I get it – I’d forgot there was draught on it..

[DiogenesParticipant @diogenes]

..forgott-en, even..

[Sarah FParticipant @sarahf]

A nice bit of machining there Jason, I have a lot to learn.

 

You mentioned that you used Alibre, does that include the CAM and Gcode generation?  I’m only used to Cut2D and Mach3.

Regards,

Sarah

[JasonBModerator @jasonb]

I just use Alibre for the design. For the CAM and G-Code Post Processor I use the free version of Fusion 360 which outputs suitable Mach3 files. I did get Cut2D with the machine but gave up on that after a couple of weeks as it did not really do what I wanted which is a fair proportion of 3D work. Even for 2 nd 2.5D it is a lot easier with the 3D image on the screen then you can just click on say the bottom of a pocket or in teh video below the top of the boss and flat areas each side of the cap to set a height rather than having to look back and find the heights.

For tonights entertainment I will cover the bearing pedestals and their caps. The original I am replicating used Babbit for the bearings but I will turn mine from bronze so the pedestals are a bit narrower to allow for flanges each side of the bearing.

Two x two blocks of 6082 were roughed out oversize on the manual mill and then located in the KX-3s vice. First I did the hump back profile and boss of the caps followed (not shown) drilling the clearance holes.

The pedestals were then located – I tend to use the top centre of the stock a lot as my datum. The basic shape cut with a 4mm 3-flute ali cutter leaving 0.3mm still to come off. The holes were then drilled and in the case of the top two tapped M3. Canging to a 4mm dia cutter with a 1mm corner radius to leave a fillet around the bottom I contoured the pedestal and then screwed the cap in place an ran the contour again at a different height which ensures all the edges match up and are perfectly flush.

Back to the manual mill to remove the excess holding material from the bottom of the pedestalls.

Then with the caps in place I drilled and reamed for the bearings. Should say 9.8mm drill and reamed 10mm, it’s the crankshaft that is 8mm! No photos of the bearings as they are just bobbin-shaped bits of bronze

 

[JasonBModerator @jasonb]

The original engines came with the two disc type crank webs as iron castings, the one I have based mine on would not turn over and one of the main reasons was that the crank had twisted at one or both of the crank pin to web joints. For this reason, I decided to make my webs from steel so that the whole crankshaft assembly could easily be silver soldered together.

The two webs were first turned, drilled and reamed 8mm on the lathe and made good use of a couple of bar ends. I used a CCGT 060208 insert to give a nice fillet to the internal corner.

The webs were then held in the 3-jaw chuck using soft jaws and the “cast” recess milled. The majority of the material was removed with a 4mm cutter using an adaptive tool path, this needed a bit of tweaking of the parameters to get the 4mm tool into the narrow gap but was done mostly by reducing the minimum cutting radius. That cutter is starting to loose it’s edge I can hear a bit more noise and it left a small burr around the edge of the cut then changing to a cutter with a 1mm corner radius the bottom of the recess was finished with a horizontal path and lastly the edges of the recess done with a contour going round twice. At about 3.00 mins in you can see that the shaprper cutter removes the burr from the earlier adaptive op.

The usual methods of a full length shaft and pin with reduced ends were use to make the other bits from PGMS which was then silver soldered together before a quick clean up skim of the webs on the lathe before the middle if the crankshaft was cut away. Quite like the black oxide from heating that has been left in the recess

All seems to fit and go round as it should. I’m not going to fit a pulley on mine so just made the crankshaft on the near side a bit longer than is needed for the eccentric as it saves a bit of shelf space!

[JasonBModerator @jasonb]

The Cylinder was cut from a block of cast iron. First I machined all the faces with a Shell mill fitted with inserts intended for Aluminium leaving 1mm on the sides, top, bottom and one end. This was then held in the mill vice and the ctr of the piston and valve bores spotted before drilling the valve hole 7.8mm and reaming out to 8mm.

Transfering it over to the 4-jaw the second spot mark was clocked true, the bore opened out with a couple of different size drills and then finish bored to 20mm. A also faced off this end where the piston rod goes at the same setting to ensure it was true to the bore.

While the cylinder was an easy to hold shape I did the rest of the details – tapped holes for cylinder and valve covers, steam passage and the notch to connect that to the cylinder. The other end was almost the same except it had a 4 hole pattern for the cylinder cover.

There was also a tappe dhole for the steam inlet and two holes to connect the valve chamber to the steam passages, the outer part of these holes is tapped M4 x 0.5 and will get plugged after the shaping has been done.

It was then onto the CNC to machine the “cast” shape of the cylinder. I did this in two stages, first the teardrop shape between the two flanges with the work horizontal and then the actual flanges with it held vertically.

The first part was done with an adaptive to remove the majority of the waste, a quick horizontal to finish the top of the inlet boss, a contour to remove metal from thinner flange faces so that the final scallop path did not drive the cutter into these vertical faces at full depth which was more than the flute length.

The “Ace of Clubs” mark you can see on the surface is the result of a tiny bit of backlash in the Z axis and is where the cutter changes from a downward cut to going back up the other side or vice versa. Probably less than 0.025mm (1thou).

I will cover the rest of the cylinder in the next update.

[DiogenesParticipant @diogenes]

A lot of iron to hog off that – a good illustration of how clean and ‘chippy’ c/cast bar is – not the source of horror that some people would have you believe..

[JasonBModerator @jasonb]

What’s that they say about broken eggs and cakes?

Best not show this one just taken with a 3-jaw chuck and a bit of CI swarf. F360 tells me there is 65% of the original metal in the swarf tray.

[JasonBModerator @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. :-[

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