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Post by William A on Nov 29, 2022 8:38:04 GMT
Thank you - turned down the wheel seats and they're good to go. I do love a bit of between-centres turning. In the meantime I've also machined up the crankpins and crankpin washers - so really, the next stage is the connecting rods. I've run into alot of heartache with some of the parts I bought that I decided to re-use because they were part machined. Generally I've made good, but one of those was the frames (hence the saga of the bent frames) and the fact that the horn slots were VERY tapered. I used a long series milling cutter to bring them straight, but the net result is that the coupled wheelbase may have shifted to accomodate this fettling and therefore is unknown.The wheelbase should be 10.750", so I used the following process to determine it: - I measured both axles at 0.750" bang-on.
- I set up the chassis in the milling vice parallel with the X axis, and dropped an edge finder on one side of one axle, found the edge, and then traversed across to the other axle and found the edge there.
- For the final >0.100 I also set up a Dial Indicator incase I needed to re-set after.
In one direction the edge finder got me 10.736" and the other it got me 10.740". Both times, the dial indicator showed 10.730". Obviously, there's some inaccuracy somewhere and I'm liable to believe the dial indicator on the off-chance that backlash is confounding my second edge-finding - but clearly I need to find another way and I really don't want to buy myself a bloody 12" caliper - any ideas? My plan unless someone can give me some direction is to find myself some spare bar and machine it to 9.990" long (i.e. the longest measurement for the wheelbase, minus two axle radii) and try to slot it between the axles in the middle of the frame. If it doesn't fit, then I'll take off 0.004" and then 0.010" and that should tell me, right?
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uuu
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Post by uuu on Nov 29, 2022 8:53:58 GMT
I suppose that would work. But without a long calliper, how are you going to measure the test bar you're making? If you're using the same milling machine to measure the bar (and to bore the holes in the rods), you might have the same ambiguity of positioning.
Wilf
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Post by springcrocus on Nov 29, 2022 9:42:49 GMT
If the question is about finding the spacings for the con rod holes, then you don't really need to know the distance in actual numbers. I'm assuming that your axles have centres machined in them and, if so, you can make one of these. Two flat bars with a bush at each end and one slotted for most of it's length. Make a pair of pins to be an accurate fit in the bushes and a pair of screws to fit the slot. The other bar has tapped holes. Offer up to the loco and lock the bars together. On your con rods, make a centre for the first hole, locate your length-finder on the rod and spot through for the other centre. Done with care, you will be suprised how accurate this can be. Regards, Steve
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uuu
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Post by uuu on Nov 29, 2022 10:40:28 GMT
I've said this before, but it bears repeating - do most of the machining of the rods before final positioning of the holes. The rods may change length by quite few thou as the shaping and/or fluting is done.
Wilf
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Post by William A on Nov 29, 2022 14:08:18 GMT
If the question is about finding the spacings for the con rod holes, then you don't really need to know the distance in actual numbers. I'm assuming that your axles have centres machined in them and, if so, you can make one of these..... Regards, Steve I'm sure Curly would approve! I'll do that - thanks! Thank you for the tip about doing the holes last Wilf, I'll make sure to do that. If a few thou confound me I think I might be in trouble, though! Here's my quick during-a-meeting CAD drawing for the centre finder:
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Post by William A on Dec 30, 2022 14:56:23 GMT
In the end I was able to get an accurate reading with my edge finder and axle method, so no need to build the sliding gauge, video here:
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Post by William A on Feb 20, 2023 9:54:12 GMT
I don't have a rotary table. Is it madness to use the old-school method of rotating the coupling rods/crank webs around a turned pinion, against a milling cutter? I've never done it before, but I don't relish the amount of hand filing, or cost for the table!!
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stevep
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Post by stevep on Feb 20, 2023 10:25:55 GMT
I have used this method William. Just take it easy. Don't try to cut off too much at one go, and for safety, wear a pair of leather gloves!
It is worth while trying to set a stop, so you rotate to the same position each time, as at the end of the rotation, you will bring to work into full contact with the milling cutter and it can 'grab'.
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mbrown
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Post by mbrown on Feb 20, 2023 10:26:31 GMT
I do have a rotary table - but I still usually do rod ends by the "old" method you describe as there is no chance of getting the radius off centre and it is much quicker to set up.
The trick is to take very small cuts in one direction only and watch closely to get the ends of the cut in the right place. If in doubt, stop a little short and finish with a file.
Make sure the pin is a mounted rigidly and is a good fit in the rod hole so it doesn't wobble out of true. And if the rod is short, rig up some sort of extension to it so that you can control it and keep your fingers away from the cutter. The main thing is to take it slowly and stay in control all the time.
You can get a really good finish this way.
Malcolm
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Post by William A on Feb 21, 2023 7:36:37 GMT
Thank you both - worth a try on some scrap material first, maybe - though a kind friend has offered to lend me a rotary table in due course too.
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Post by chris vine on Feb 21, 2023 9:32:31 GMT
Hi William,
A good trick to finishing the profile after milling etc, is to use the pillar drill with an abrasive in the chuck and use the table to guide the rod as you work it around the spinning abrasive.
Top tool is something like a spiraband on a rubber mandrel. Or, in a few minutes, you can make a mandrel, say 1/4" diameter with a slot across the end. Then you just put in a bit of "emery" tape and wind it round. As the end bit gets worn out, you can tear it off and continue. You can get a really lovely finish and take out any little imperfections in milling in only a few minutes.
By using the pillar drill and table, the work will stay true to the tool and you won't get rounded corners.
It does help if your drill has a fairly high speed, but it isn't important.
Chris.
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Post by GWRdriver on Feb 27, 2023 13:23:35 GMT
While I fully sympathize with wanting to avoid the filing labor, I would have to weight in on the side of madness to mill rod ends by hand rotation. I would never attempt it. Not that it can't or hasn't been done, but because the technique is fraught with peril, opportunities to ruin both work and fingers.
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stevep
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Post by stevep on Feb 27, 2023 15:45:02 GMT
Harry, I have GH Thomas small rotary table, which is not geared. So the rotation of the table is done by means of a screw-in handle - not much different in length to a loco connecting rod. It works absolutely fine, provided you follow my previous advice - don't try and cut too much at a time, and set up a stop so that you turn to the same spot each time. Here is a picture of it being used to round off the backs of the eccentric straps on my Pansy.
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Post by davewoo on Feb 27, 2023 18:05:48 GMT
I've got the little GHT rotary table, and agree with Steve about it's usefulness, used far more than my large rotary table, the stops are a genius feature, I've done countless rods, valve gear parts etc over the years and think it's one of the most useful of GHT's tools I've made. When first made I only had an ML7 and vertical slide so left out the T slots and used a matrix of 5mm tapped holes in the table and no graduations around the table. At a slack time at work made a new T slotted table with graduations , I actually regret this as clamping was easier with the tapped holes, and I've never used the graduations. Castings are available but mine is made from chunks of steel, gave the little myford a hard time! Well worth the effort of making.
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Post by GWRdriver on Feb 28, 2023 3:52:58 GMT
Harry, I have GH Thomas small rotary table, which is not geared. So the rotation of the table is done by means of a screw-in handle - And it looks to be a very handy device indeed, Steve, I like to stops feature, but then that's quite an improvement over the rod end on a fixed pin rotated with the fingers, which is what I had in mind. Having had my share of instantaneous scrap being created by climbing milling cutters . . . I get a little twitch if I even think of repeating one of them.
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Post by William A on Apr 22, 2023 20:18:17 GMT
Lumbering forward with the build, crank webs done!
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Post by William A on May 8, 2023 7:04:25 GMT
The pins on the crank axle were very good fits, but I've still ended up with bloody problems with my crank axle Is it enough that I can turn it with finger pressure on the axle stubs or does it need to be re-made? I can't quite work out what's gone wrong - the webs are within a thou or two of being parallel and I can't see any daylight when I use an engineers square against the stub axles - maybe the middle axle hasn't gone on straight somehow?
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tony9f
Involved Member
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Post by tony9f on May 8, 2023 9:21:41 GMT
Hi William,
I feel your frustration, I have sent you a PM.
Tony
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Post by ettingtonliam on May 8, 2023 12:38:03 GMT
You are testing it running between centres, but the centre drillings have no significance in the final axle. You should try, if you can, running the axle using the bearing surfaces to mount it on, then seeing what if anything runs 'out'
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uuu
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Post by uuu on May 8, 2023 12:45:14 GMT
Also, in your video, you note how much the middle is oscillating - but this bit doesn't matter - it's the journals and the wheel seats that you want to be true - these seem to have less runout.
You may not improve things with another go - unless you change your approach to build up everything on a single bar, then cut away between the crank cheeks.
Wilf
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