Author Topic: PM Research Engine Number 1  (Read 42820 times)

Offline propforward

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Re: PM Research Engine Number 1
« Reply #120 on: September 20, 2020, 03:47:09 PM »
Got a little drilling done first anyway.



Stuart

Forging ahead regardless.

Offline gary.a.ayres

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Re: PM Research Engine Number 1
« Reply #121 on: September 20, 2020, 07:30:15 PM »
Very neat.

BTW I appreciate you may have used a DRO before, but if not I think you will love it. It's also worth investing in an electronic edge finder. If you haven't seen them mine is featured on my uniflow thread. It's much easier than peering at a wobbler and it looks pleasingly sci-fi too.    :)

Offline propforward

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Re: PM Research Engine Number 1
« Reply #122 on: September 20, 2020, 10:17:09 PM »
Excellent point Gary! In fact I read your post with extreme interest last night - that is a great looking piece of kit, and I enjoyed your description.

In the end I decided to go the "whole hog" on the DRO, and bought a DRO pros EL700 4 axis set up, and also ordered the integrated touch probe.

https://www.dropros.com/DRO_PROS_Touch_Probe.htm

I have heard some mixed reviews on their touch probe as supplied, but apparently if you upgrade it to a steel tip, it is very reliable and accurate. Sure hope so. I sometimes wonder about the wisdom of adding so much instrumentation to a basic mill like this - it's more than half the cost of the machine. But I think it will add a lot too. Hoping I won't ever need another machine tool - although if a good Bridgeport comes along, then that could change I suppose - although I really don't need that much mill. I haven't come close to using up all the table on mine  - except when I had 3 different set ups mounted on it, and that was great. Vise in the middle, rotary table on the left, angle plate on the right. Magic, our Morris.
Stuart

Forging ahead regardless.

Offline gary.a.ayres

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Re: PM Research Engine Number 1
« Reply #123 on: September 20, 2020, 10:48:13 PM »
Stuart -

I suspect that you will not regret your purchase. You will be enjoying your setup long after you have forgotten about the spend. A DRO makes life a lot easier. The touch probe looks much more delicate than my electronic edge finder and so may be more sensitive. And your mill is decent so it's worth upgrading while you wait for the Bridgeport of your dreams to come along. Which will also need upgrading...  ;)

I too quite like to keep a vice and a rotary table as semi-permanent fixtures on the mill. Saves a lot of chopping and changing, that being probably the most time-consuming part of what we do.

For me, though, mill size isn't so much about table space as it is about spindle nose to table distance. That's the one that usually leaves me scratching my head for alternative solutions...

Cheers,

gary

Offline propforward

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Re: PM Research Engine Number 1
« Reply #124 on: October 22, 2020, 10:01:07 PM »
Well I'm loving the new mill upgrade, and I'm glad I made myself finish that before proceeding with the engine. It has made today's progress a lot more enjoyable.

I decided to add the stepped feature to the bearing caps. Not really necessary, and most builds I have read leave this out, but I figured why not give it a try?





Then I moved on to machining the bearing area on the base casting. I have been having trouble getting my head around how to locate the surface of the bearing area when at an angle. I couldn't figure out how to locate it relative to the center of the bore in the cylinder mounting. But then when I was at work I saw one of our machinists setting up an extremely complex item, and he was showing me how to use gauge blocks and pins to set up different features. Armed with this fresh insight, I was ready to have a crack at this base casting again.

I set up my angle block, getting it mostly square to the machine using a 2-4-6 block in my vise, which I had already trued up. I used the dial gauge to verify squareness of the angle block.



....and checked angle using this caliper. This was a gift from a small business I helped out with some design work. It's a handy tool, but not sure I'd splurge on it normally.



Before setting up the base casting, I used a pin gauge to verify the bore diameter in the end of the casting, and then used the pin gauge to measure height of the rail surfaces relative to the bore.



I didn't take a picture, but I did the same thing to establish the center of the bore relative to the guide rail edges.

Then I moved it to the mill and finished the set up - I clamped it to the angle plate and then clocked it to verify squareness again.



In this next picture, you can see a gauge block and a pin gauge in place against the machined surface where the guide gland goes. Using this, I was able to touch off against the top of the pin gauge, and establish a height to the top of the bearing surfaces. I could also calculate the position of the center of the crankshaft. Easy as it turns out - just some trigonometry. In the picture you can see a spot face and center mark I made some months ago, when I was trying to figure out how to do this. I made the center mark as a visual aid.



 Anyway - decided to have the courage of my convictions and went for it.





The bearing caps fit reasonably well.



One thing to notice is that because of an earlier error when machining the face where the cylinder mounts, the bearing caps are not perfectly located. I did not properly interpret the intent of the design and did not locate the mounting face of the cylinder correctly relative to the datum on the print. As a result I have had to machine more away from the bearings on the base casting than is ideal. I knew this was going to be the case, at this point I am continuing on, correcting things as I go, with a lesson learned. This should still work - it will always look a bit odd, but it's only my third engine, and 1st casting set. There are bound to be learning opportunities along the way. The next one will be better, for now forge ahead.

I'm pretty happy with how the bearing caps fit anyway.

I clamped the caps in place one at a time, and spot faced through the bolt holes, before drilling a tap hole for the screws, and tapping the threads.



Then screwed the caps in place.



After that, I cleaned up the outside and inside faces.



Normally the clean up would be done after bolting the part flat to the table - but I decided this was as valid a method as any, and looks a little "different". Odd? I don't know - put my own slant on it. Slant. Get it?

Anyway, I also dusted off the front edges of the caps to make them match up to the base casting a little better.





After that, I removed the part from the angle plate, and decided this was good a time as any to spot and drill the bearing caps for the oilers.



This is where it sits now. It is FAR from perfect. It can, at best, be described as adequate, but while that is true, there are a lot of successes on this part, in terms of setting up square and true, and learning how to indicate off available surfaces to establish geometries. I am actually very pleased. I was at least savvy enough to not just press ahead assuming everything was right, but measured the part to find out where I was at - as such I think I can recover it and make a working engine.



The two slide rails for example, are off center. But I now have the option to machine the wider one to match the narrow one, and get them both centered. Alternatively I'll machine the guide to suit. Once in place the difference in rails will not be obvious. So I need to give that some thought. Either approach means making mating parts fit what I have, and not achieving parts that are "made to print", which is a goal of mine - but I'm making progress, and enjoying myself. Therefore, I deem it a success, at least on some level.

Next - get the casting set up and drill and ream the bore for the crank shaft.

 :ThumbsUp:



Stuart

Forging ahead regardless.

Offline gary.a.ayres

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Re: PM Research Engine Number 1
« Reply #125 on: October 22, 2020, 10:26:50 PM »
Very interesting measuring techniques and setups, at least to a neophyte like me.

I like your undaunted spirit and willingness to accommodate imperfections, keeping the momentum of the project while learning and looking forward to the next build being better.

Offline propforward

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Re: PM Research Engine Number 1
« Reply #126 on: October 22, 2020, 10:49:04 PM »
Thanks Gary. I'm just trying to make use of what I see others do - it has been humbling at times, along the way, but a certain amount of dogged sheer bloody mindedness sometimes gets you through. It's easy to become discouraged - after all these parts I have made are not "right", but hopefully I am improving along the way, so subsequent engines will get better and better. That's the idea anyway. :D

Case in point, I went ahead and drilled and reamed the bore for the crankshaft.

It's close, but there's a mismatch somewhere. Need to evaluate my techniques more. But in the meantime I'll soldier on.



You can see how the nearside is mostly aligned, but the far side interior surface looks off - result of that error made much earlier on that I mentioned.



And sure enough, once the bearing cap is removed, the hole is way off center relative to the locating steps, and indeed a little off height wise, but not by much.



I think it will run. I did not seem to get any "wandering drill" when I drilled all the way through the second side - I drilled the hole out in steps, leaving some stock to clean out with the reamer. So I am confident that the bore is centered height wise to the rails. I will measure that and check.

However, going to call this "acceptable (just)" and keep going. Not sure what to do next - maybe a few of the simpler components, like upper slide rails and spacers.
Stuart

Forging ahead regardless.

Offline propforward

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Re: PM Research Engine Number 1
« Reply #127 on: October 22, 2020, 11:36:32 PM »
I think I either measured the rails position incorrectly, or established my zero for this op incorrectly. My bet is on a measurement error. You live and learn. Onwards and upwards. You’ve only got to be a few thou off for things to look very noticeable. I think my gauge block and gauge pin approach basically worked.

If my angle plate was off, that could throw things off position - maybe that’s the culprit.

Ruminating on it more, I am most suspicious of that angle plate, and possibly the way I set height of the milling cutter against the gauge pin.

It is all anout the set ups!
« Last Edit: October 23, 2020, 12:28:41 PM by propforward »
Stuart

Forging ahead regardless.

Offline MJM460

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Re: PM Research Engine Number 1
« Reply #128 on: October 23, 2020, 12:28:09 PM »
Hi Propforward, as another working on castings for the first time, I can empathise with all those problems.

You are certainly making great progress.  Those components do not look easy to hold, but are coming out well.

Measurement, like so many things, is simple in principle, but as I try and achieve more accurate, I find it more and more difficult to actually do.  It takes lots of practice.  I never cease to admire the work of those who seem regularly to achieve 0.0001”. About 0.001”, or even 0.01 mm is about my limit at the moment and that is only achieved occasionally.  Drilling a hole is easy, getting it in the right place is quite difficult.

MJM460

The more I learn, the more I find that I still have to learn!

Offline propforward

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Re: PM Research Engine Number 1
« Reply #129 on: October 23, 2020, 01:31:41 PM »
Hi MJM, thanks for looking in. I concur with your sentiments! There are those that make this look very easy, but the level of attention to detail needed makes it anything but. That's why I like this hobby - it's a real challenge. Although I haven't done (in all honesty) a very good job on this engine so far, it is still immensely satisfying. I read everyones threads and pick up tips wherever I can. The posts I like most are those that really detail the set up aand measurement arrangements. Great to have access to a forum like this.
Stuart

Forging ahead regardless.

Offline propforward

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Re: PM Research Engine Number 1
« Reply #130 on: October 23, 2020, 01:35:34 PM »
One habit I need to develop more is spotting locations and checking, before forging ahead.
Stuart

Forging ahead regardless.

Offline propforward

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Re: PM Research Engine Number 1
« Reply #131 on: October 23, 2020, 10:48:54 PM »
I checked the crankshaft bores with a gauge pin today. It's .002 oversize, which surprises me a bit given that the hole was reamed, and in a single set up without ever moving the table. Still, that's OK, I will make the crankshaft to suit.



The bore may not be as far off center as I had thought. Looking at it here with the gauge pin in place, the center of the pin seems to fall pretty close to the split line at the bottom of the bearing cap locating slot. I didn't need to chamfer the edges or anything to get the pin in - it popped right in  from the top, so I think I'm not as far off as I thought. The only mystery is the difference in width of the locating slots. Maybe I'll just pretend that's an orientation feature.



Anyway, time to move on. Tomorrow............not sure, but I'm thinking the cross slide rails and guide.
Stuart

Forging ahead regardless.

Offline AOG

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Re: PM Research Engine Number 1
« Reply #132 on: October 24, 2020, 03:01:22 AM »
I think what you are looking at is a slight unevenness in the casting. You won’t even notice it when it’s painted. I also wouldn’t worry about the oversized holes. You can get dimensional changes just from the heat generated by the operation. In any case, when you make your crankshaft you are aiming for a running fit so you are going to want 1 to 1.5 thousandths gap between the shaft and the hole to get a good oil film between the parts. In any case you are going about this the right way. I find it easier to make the hole and tailor the shaft to the final size of the hole than doing it the other way around.

My 2 cents

Tony

Offline propforward

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Re: PM Research Engine Number 1
« Reply #133 on: October 24, 2020, 10:53:50 AM »
Thanks Tony - solid advice, and I appreciate your looking in. Very helpful - that gives me a dimension to shoot for on the crankshaft for a nice runner.
Stuart

Forging ahead regardless.

Offline propforward

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Re: PM Research Engine Number 1
« Reply #134 on: October 24, 2020, 10:58:55 AM »
I should point out that machining the outside surfaces of the base casting by the bearings was not required - only the interior surfaces locate the crankshaft. But I felt like doing it because it blends in the outside edge of the bearing cap to the base. Looks a little neater is all (in my opinion).
Stuart

Forging ahead regardless.

 

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