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Post by brucevoelkerding on May 10, 2023 12:26:01 GMT
Another way to profile the Coupling Rod ends is to get a Shoulder Screw which fits the hole in the Coupling Rod. Here in the States one can buy Shoulder Screws with a "precision" fit. In the size you would probably use a "standard" Shoulder Screw is made -.002/-.004" diameter. A "precision" Shoulder Screw is made .000/-.001" diameter. A "precision" fit would be best. Mount a piece of cold drawn Flat Stock, say 3/8" x 2" x (length not critical) in the Mill Vice. Top Surface of the Plate must be above Vice Jaws. Drill & Ream a Hole to fit the Shoulder Screw. Make a Spacer Washer on the Lathe which fits the Shoulder Screw and is the Diameter of the Coupling Rod end. Set the Spacer Washer on the Plate in the Mill Vice, set the Coupling Rod over it, assemble all with the Shoulder Screw. Note you will need a Washer and Nut for the bottom of the Shoulder Screw. This is the Reason for using the 2" wide Plate in the Mill Vice - to be able to sneak your Wrench in to tighten the Shoulder Screw. Make your Spacer Washer so that the Shoulder Screw can be tightened - the Coupling Rod is NOT rotated against the Cutter as described above.
Put a suitable End Mill in the Mill and offset the X-Axis as required. With the Shoulder Screw TIGHT, plunge the Mill Spindle DOWN, loosen the Shoulder Screw, rotate the Coupling Rod, tighten the Shoulder Screw, repeat. It does go a lot faster than it sounds. I do a rough pass at a slightly increased Radius followed by a finish Pass at the correct Radius. You can get as close as you dare to the Radius of the Spacer Washer but try not to cut it (you would then be undersize).
To remove the little Ridges, I file. I would have made qty 2 Spacer Washers above to use as Filing Buttons. I grind the end of the File such that there are cutting Teeth the entire end of the File plus I add a polished radius (approx 1/16" Rad) at the End so the File does not dig into the Coupling Rod proper or the Oil Box. It doesn't take long to get rid of the Ridges. I make a Pin the length of the Coupling Rod plus the 2 Spacer Washers plus .025". I place the assembled parts in the Bench Vice. You will be able to freely swing the Coupling Rod and the Filing Buttons are free to rotate. Hold the Coupling Rod in one Hand, the File in the other and go at it. It's a feeling of accomplishment when the File stops cutting and just ROLLS the Filing Buttons. It helps to have a selection of wood Blocks to stop the swinging of the Coupling Rods when filing near the Rod proper or the Oil Box. Note I do not file ACROSS the Coupling Rod end, rather I file lengthwise (in the long direction of the Coupling Rod).
Note there is absolutely no need to harden the Filing Buttons since they are free to rotate. I have used sets of them repeatedly.
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
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Post by kipford on May 10, 2023 16:24:55 GMT
William Take heart it took me three attempts to get my crank axle made. One thing I do though is to make the crank up with a solid axle as Wilf suggests. Attempt 1 was scrapped when on the final operation I attempted to mill a big away from the webs rather than the unwanted bit of crank axle. Second one for some reason ended up with a lot of run out. Finally on the third attempt it all went well. The one lesson I have learnt during my Aspinall journey is first do not rush, second if you are not happy with the result bin it and start again, the second one is always quicker as most of the thinking has already been done. Dave
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jma1009
Elder Statesman
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Post by jma1009 on May 10, 2023 23:13:44 GMT
I think you have misunderstood the shouldered joints which are for press fits, and probably as dodgy to do on a crank axle with a dodgy outcome.
As Wilf has helpfully suggested, a loctited crank axle can use a solid axle without shoulders, then cut out the bits between the crank webs after the loctite has cured.
I think that your sliding fits are a bit on the slack side, and you could have used the ‘cotton reel’ method.
However, it’s not a bad job, and I wouldn’t consign it to the scrap bin. I’ve seen far worse crank axles running around club tracks for over 30 years without any undue consequences.
Cheers, Julian
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Post by William A on Jun 9, 2023 11:31:53 GMT
I think I have finally cracked the crank axle - what a palaver!
I re-made all of the pins/axles and (save one joint) shrank-fit them instead of loctiting - and it's gone alot better...
All of the pins are 0.002" over the nominal bore - is that fine, or am I going to need to cross pin? Curly suggests 0.001" over bore without a pin but just want to make sure this isn't something that painful experience has been gained elsewhere.
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Post by William A on Jun 11, 2023 7:08:51 GMT
Do you reckon I should cross pin the webs too? I've gone at least 1.5 thou over nominal on the pin shanks so in theory that should be sufficient, right? Curly Lawrence doesn't indicate anything about pinning...
They're only 1/4" thick so I guess a 1/16" or 3/32" pin? Going all the way through (1-1/4") feels like a big ask as I'll have to hold the axle freehand on the mill rather than clamping....
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uuu
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Post by uuu on Jun 11, 2023 7:29:38 GMT
That sounds too precarious to me. If you could clamp - and had really steady feed control, then the extra peace of mind might be worth the angst. I'd leave it and move on.
Wilf
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Post by William A on Jun 15, 2023 6:08:08 GMT
Thanks, Wilf - I think that's the conclusion I've come to too!
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Post by William A on Jun 23, 2023 8:29:27 GMT
I've tried to grind up my first d-bit reamer to use on the water pump valve box but it's been a bit of a failure. I took the following steps:
1) Grind away 1/2" the diameter on the end of some silver steel 2) Add a relief on the to the end, rear and bottom of the 'D' 3) Use a diamond hone to ensure a sharp cutting corner
I'm only cutting into bronze, but the tool did nothing but rub and squeak. Googling this information is tough because it leads me towards D-Bit Grinder tools, rather than grinding D-bits by hand.
I know it's hardly neccesary in this day and age of disposable slot drills and cheap reamers but I would like to know what I'm doing wrong. Is there an obvious way to troubleshoot the problem with the cutter?
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tony9f
Involved Member
Posts: 95
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Post by tony9f on Jun 23, 2023 9:21:39 GMT
Hi William,
A couple of things; Bronze is a bugger to machine anyway. Have you drilled out the surplus metal prior to reaming which will assist the cutting action as it gives less resistance to the tool? When you say bronze, is it phosphor bronze, Colphos 90, SAE 660 or gunmetal? Phosphor bronze (red coloured) is very resistant to machining and needs very sharp tools. It also tends to bind on drills and reamers and benefits from lower cutting speeds. As for making D bits, the essential thing is that the tool is thinned to exactly half the diameter and that the flat surface is actually flat and as I'm sure you are aware the usual procedure is to file down the end to within a couple of thou of the centre line, harden and temper then finish the flat on an oilstone until it is half the diameter. I tend to grind the end relief at an angle of up to 5 degrees leaving as sharp an edge as possible. This should be adequate to achieve the results you are looking for.
I hope that this helps and I'm sure that there is a wealth of advice out there that others can give you but so far it has worked for me.
Cheers
Tony
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Post by ettingtonliam on Jun 23, 2023 11:12:44 GMT
Sorry if this is obvious, but the end relief needs to go 2 different ways, each side of centre, otherwise it rubs and won't cut---.
Wilf is right, drawn phosphor bronze is a real b----r, I try to avoid it wherever possible
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uuu
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Post by uuu on Jun 23, 2023 11:58:59 GMT
Here's a video which appears to be relevant: YouTubeWilf
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Post by William A on Jun 25, 2023 8:00:33 GMT
Thank you all, I did watch that video too. I ended up using a 5/16" slot drill to clear most of the material and ending with the 11/32" d-bit. Or rather not - because it mostly just rubbed and created dust. I'll review my technique, the only thing I can think is that I went slightly under the centreline (I used the radius of the grinding wheel to create top rake, then underneath the cutting edge, then on the tip). I'll try on something more easily machineable.
It was/is a bronze casting and made a habit of snatching drills - and I didn't have spare drills in the required sizes to regrind (another rabbit hole no doubt).
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Post by William A on Aug 31, 2023 12:45:40 GMT
There's been a bit of a hiatus on this - I was trying to mill out the flute of my connecting rods and had a series of confounding problems with the horizontal arbour of my mill. I think that's sown up now, but I need to set it up and want to do so again properly. I haven't given up!
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