Author Topic: JC attempts the MEM Corliss  (Read 3129 times)

Offline crueby

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Re: JC attempts the MEM Corliss
« Reply #30 on: December 09, 2020, 11:44:30 PM »
Got an excellent finish with the fly cutter!

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #31 on: January 03, 2021, 08:39:43 AM »
After a bout of Covid 19, it was time to do something in the workshop again. I decided to bore the cylinder. Up till now I had better results on the lathe with HSS tool bits compared to carbide inserts. So I had to make a HSS boring bar. I like the boring bars made by Stefan Gotteswinter (https://youtu.be/O9d_I0A4kzg), so I first had to make a tool to make a tool - a slitting saw arbour (also according to a design by Stefan) to cut a slit for the boring bar.

Unfortunately I only had 10mm round stock for the bar, and all the suppliers are closed for the summer break. Would have preferred it a bit thicker.



After facing the cylinder block on the lathe, I drilled out the cylinder to the maximum diameter drill I have, and then started boring with a carbide insert (lots of chatter) until the hole was big enough to accept my brand new boring bar with its freshly ground 4mm HHS bit.





Roughing out went smoothly, my boring bar is working! No chatter. As I approached the final dimension, I rounded the tool bit a little bit with a stone, reduced the depth of cut, and decreased the feed rate, expecting a very smooth surface finish as the result. Big mistake! Steep learning curve! The tool immediately started to chatter. Being close to final dimension, I had to stop boring. Should have started experimenting earlier! Due to the small depth of cut, the chatter marks are relative small though. I am now curious to see if lapping will remove the chatter marks and leave a smooth finish. As soon as I can find a 3mm sheet of copper I will attempt lapping by following Tug's thread http://www.modelenginemaker.com/index.php/topic,1908.0.html.

But before lapping, I first have to drill the inlet and exhaust holes.

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #32 on: January 03, 2021, 09:24:43 AM »
I decided to follow Vince's approach to drill the port holes. But first another tool had to be made - a lathe stop. I followed Joe Pieczynski's design (https://youtu.be/LrCS_-3Gh0Y). I also made a 15 deg reference plate for the vice, and then proceeded to mill 3mm flats for the drill bit to start on.



Then it was time for the first 1.5mm hole. I spot drilled with a 90deg spot drill, held my breath and started drilling. At about 8mm depth, the drill broke.



This is not going to work. The maximum speed of my mill (Rong Fu 45 clone) is only 1600 RPM, the total runout is about 30 micron, and of course there is no feel for what the drill bit is doing. And the required depth of a hole is more than 12 mm.

So what to do? At this point I think it will be better to first drill the valve holes, mill the steam pockets, and only then drill the small holes, which then only has a depth of about 2mm. I am also contemplating to buy or make a micro drill adapter which allows feeding the drill by hand while still being driven by the mill, as demonstrated here (https://youtu.be/PqU5wS0J4MU). Another alternative would be to use my home made CNC router (which has so far only been used for milling wood). It has a variable spindle speed from 5000 to 20000 RPM.

I do not think it will be possible to remove the broken drill bit. On the bright side - at least now I have a cylinder block to try out different drilling strategies, and also practise lapping.

Any advice will be much appreciated.

Offline Ramon

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Re: JC attempts the MEM Corliss
« Reply #33 on: January 03, 2021, 09:54:38 AM »
Hi JC,

Commiserations on that broken drill - not the best place to be at any time. Still it looks recoverable.

My thoughts would be to forget the broken drill and use a slightly larger drill to do the remaining holes within the limits of the slot - 2 -2.2mm maybe and drill slowly (feed) at your max revs. 1600 rpm may not be text book but should be more than sufficient. Lots of small pecks and withdrawal to clear the swarf is needed on this situation. It doesn't take much swarf to jam a small drill and that's a deep hole relevant to diameter. Keeping the swarf clear is something to keep in mind at all times here

You could use a carbide drill to try to remove the broken one but given where it is and the little effect it will have on the final running personally I wouldn't bother - you could end up making things worse which is always a risk. Increasing the diameter of the holes will easily make up for any loss of flow. Annoying to think it's there though but once covered - 'out of sight out of mind' soon makes it forgotten about  ::)

Your mill looks very similar to my Amadeal so I assume you have a drill spindle function. It has to be said that mine is 'heavy' in feel compared to my drill which does affect feel on using small drills but with care this op should be manageable as set up.

Hope that's not teaching granny etc -

Good luck with it - and that lapping  ;)

Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline astroud

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Re: JC attempts the MEM Corliss
« Reply #34 on: January 03, 2021, 11:22:25 AM »
I drilled out the valve holes and milled the valve chambers before drilling the valve passages. However it was still a fraught operation as the drill then starts on the curved surface of the valve hole and starts to dance unless extreme care is taken. A very light touch is needed to allow the drill to centre.

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #35 on: January 07, 2021, 09:03:19 AM »
Tug:
Thanks for the feedback. It made me realise that the cylinder block is not lost, and I should be able to recover from the broken drill bit. I also realised that it should still be possible to dislodge the broken bit when machining the steam pocket.

astroud:
Thanks for the info. I will never have a light touch with my milling machine. I therefor decided to order a sensitive drill attachment from LittleMachineShop in the USA, which allows one to feed the drill by hand. Hope this will solve my problem. It is just frustrating that none of these more specialised tools are available in South Africa.

In the mean time I found some 2mm copper sheet at the local scrap yard, and made a cylinder lapping tool. Thanks again for your info Tug! I am not familiar with silver soldering, so I glued the copper tube to the leading edge of the D-section using two part epoxy. This is working well.



I could not resist trying out the lapping tool even before for the steam ports have been drilled. I used some fine automative grinding paste, and the chatter marks quickly disappeared. I followed this with some polishing compound that I happen to have in the workshop. The cylinder is not perfect yet, but much better than before. As far as I can tell with my telescoping inside micrometer, the bore is as parallel as I can measure.



« Last Edit: February 08, 2021, 09:02:21 PM by JCvdW »

Offline Ramon

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Re: JC attempts the MEM Corliss
« Reply #36 on: January 08, 2021, 09:53:22 PM »
Nice work on the lapping JC  :ThumbsUp:  good to note that epoxy did the trick too. Silver soldering is always a bit fraught in case it runs to far.

Keep it coming

Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #37 on: January 19, 2021, 07:29:53 PM »
Thanks for the encouragement Tug!

While waiting for the sensitive drill attachment to arrive, I made the outrigger bearing pedestal. I treated myself to a rotary table for Christmas and thought the round corners of the pedestal base to be a good opportunity to try out my new toy. I mounted the four yaw chuck on the rotary table to hold the part.







Unfortunately, the corner radii came out too large, so I will have to remake the part. It never the less turned out to be a good practice run with the rotary table and also to practice some filing and sanding to remove machining marks from a milled part. Next time I will machine the corners first, while the part is much more sturdy to clamp in the rotary table. I will also use some shim stock packing to prevent clamping marks.


 

« Last Edit: January 19, 2021, 07:46:55 PM by JCvdW »

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #38 on: January 19, 2021, 07:46:05 PM »
The sensitive drill attachment arrived today. Made in China, imported from the USA... There is quite a bit of play in the sliding mechanism, so I was a bit sceptical at first. After successfully drilling ten 1.5mm holes through a 10mm piece of scrap mild steel, I however feel much more confident to drill the cylinder block. One directly feels what the drill is doing. If the drill bit gets stuck as it breaks through, it simply spins in the small chuck, without breaking.






Offline Ramon

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Re: JC attempts the MEM Corliss
« Reply #39 on: January 19, 2021, 08:45:51 PM »
Hi JC,

Something that did occur to me and perhaps worth mentioning before you have another go at drilling the cylinder.

Did you just centre drill on an angled surface with cylinder set at the angle or did you create a flat bottom square to the drill before centre drilling. If the surface was at an angle, despite being centre drilled that can kick a drill off - it would be best to plunge a small cutter in to bring the surface level to the drilling direction before centre drilling.

Good luck with it  :ThumbsUp:

Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline crueby

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Re: JC attempts the MEM Corliss
« Reply #40 on: January 19, 2021, 09:44:08 PM »
JC, how does the sensitive drill attachment work - is there a clutch in it, or are you adding pressure with that ring?

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #41 on: January 20, 2021, 10:18:51 AM »
JC, how does the sensitive drill attachment work - is there a clutch in it, or are you adding pressure with that ring?

The attachment has a spring loaded telescopic shaft to drive the chuck from the mill. The external ring is attached to the movable shaft with a bearing. One holds the external ring by hand to apply down force on drill bit. Total available downward movement is about 24 mm.

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #42 on: February 08, 2021, 08:40:32 PM »
Tug, thanks for the suggestion. I did mill a flat surface in the cylinder block with a 3mm end mill before drilling.

Working on the bearing pedestal made me realise that I need more practice on the mill before taking on the more complex parts. So I postponed further work on the cylinder block for a while.

I had another go at the bearing pedestal, with a much more satisfying end result. A coat of primer, and it is ready for storage. I never expected making these parts will take so long, so it will probably remain in storage for quite a while ...



« Last Edit: February 08, 2021, 08:59:15 PM by JCvdW »

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #43 on: February 08, 2021, 08:57:12 PM »
I decided to make the cylinder feet next. Relatively simple parts to gain more experience with the mill. I have realised by now that starting out with correctly dimensioned and squared stock, makes life much easier further down the line. It also became apparent that I can do with a set of parallels for the vice, rather than the piece of steel ruler that I am currently using.

I went for the split design of the feet, for easier assembly later.









A coat of primer will hide any minor remaining machining marks, so I am happy with the feet so far.

Offline JCvdW

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Re: JC attempts the MEM Corliss
« Reply #44 on: February 26, 2021, 03:24:56 PM »
I finally finished the two cylinder feet. I keep on surprising myself with how easy it is to make a silly mistake. I drilled one of the feet mounting holes too big. Rather than remaking the part (for the third time!) I made a plug and Loctite it into the oversize hole.



A coat of primer to keep the rust away, and the feet are ready for future assembly.