Even though I said I'd move onto the cab next I thought the various leaf spring brackets might be a good exercise in CNC so I drew them up.
A few warning bells started going off when the drawing had a lot of dimensions missing and notes like 'spot through from frames'. We've covered my inability to spot through holes with anything like acceptable results. The missing dimensions aren't a problem - they're not critical and I hope I have arrived at workable numbers. The designer probably thought if we got this far we should be able to figure it out.
I went to investigate and found I had left myself quite a job! This isn't due to the design, just my lack of foresight.
First stop was my CAD drawings of the frames we used to get them cut. None of the spring bracket holes are on them. I assume what happened was the designer hadn't decided on how to do it at the time of the CAD drawing and got far enough into his build to do the leaf springs, decided where the holes should go, then drilled them into the rest of the sets of frames we bought off him so we didn't have to do it.
Over to the frames to measure the holes. They're surrounded by wheels, cross heads, slide bars, and valve gear. I stick some drills into them and measure across the drills but can't get an accurate number.
Seeing how crowded it is I check whether I can actually spot through if there is no alternative and sure enough I cannot. I could do the two holes above the axleboxes through the wheel spokes, but that seems like a bad idea given my past performances in this caper. In any case I cannot spot the holes for the brackets to either side because they are obscured by the wheel rim, meaning I would not be able to get the bolts into them even if I can do the holes in the brackets!
So, due to my desire to avoid these springs for as long as possible I've left myself no alternative but to drop the front and middle axles, which of course includes all the rods and the valve gear! It also means taking the brakes off and the cylinder drain operating lever.
Off come the rods - marvel at the clearance that just allows the rod to pass between the slide bars! There aren't many gnat's whiskers in that.
So from a running loco with cylinder drains and nearly a lubricator I am reduced to this:
The holes are now easily accessible and measuring them up none of them are at constant spacing - variations of about .3mm. So now it's back to measuring as best I can and then either spotting through after all or figuring what the best centres are to match all 4 sets, drilling and tapping the brackets at those spacings and enlarging the holes in the frames.
One benefit is I can give the frames a good clean, especially if I drop the rear wheels. I'm considering taking the cylinders out but it means I'll lose the valve timing because they won't go through the frames with the valve spindles in them.
For measuring the centre distance between two holes, even if they are different diameters to a reasonable degree of accuracy I use the following method. Find two rods that are a snug fit in the holes. Then use calipers to measure the inside and outside measurements between and over the pins close to the face. Then take the average. Do it a couple of times to make sure. It'd you're measuring something precisely made, round it to the nearest measurement if it's close.
If you need to measure a series of random (hand created) holes then I'd use the mill as a CMM. Clock up the piece so you know it's parallel to one of the machines axes. Then turn up a pin that's snug in the holes and add a generous chamfer. Fit it in the spindle so there's say 20mmm sticking out then jog to each hole, getting it to the point where you can jog the Z-axis to drop the pin in each hole. On each hole, set the clock against the side of the pin, first in the X axis direction and then in the Y. The idea is that you watch the clock as the pin is lowered into the hole. Correct the machine position until the pin goes in without deflecting the clock. Yes, it's slow and painful, but it's possible to measure the hole centres to better than 10 microns with ease. Just remember that if you use these coordinates to drill a matching part, you have to remember which way up you're drilling them!
Of course, you can use this technique for measuring using any mill that has a DRO
I am using the two pin method. A #36 drill seems right. The frames are only 3mm thick so the drills have a lot of movement but as you say I'm taking numerous readings.
The other method does sound very accurate!
Hi David, Be sure to measure both inside and out, not just over the outside less the diameter. Doing it inside and out, you accommodate any small amount of slack in the pins which gets nulled out by being pulled both ways.
Another way is to clamp a length of steel inside the frames, make sure it's wide enough to line up with either the top (or bottom, whichever is closest) edge of the frames, this gives you a 'datum'. You can then use a transfer punch to mark the hole centers. Remove the steel, set it up running parallel to one of the mill's axis and drill the holes of the correct size, make a note of the distance moved along the axis between the two holes. Then put the steel back onto the frames and check that two bolts can secure it to the frames without any tight spots and that the datum has remained true. In most cases, this should do the job, if the holes are slightly out, just set another piece of steel of the same width in the same position the first was held to the bed and adjust the axis distance by how much you think you are short/long. Once happy you can use this steel as a jig for drilling into the parts required.
Last night I cut the brackets down to 6mm of 7mm depth because I wasn't sure I was going to clear the vise jaws. Measuring it this morning told me I had 0.5mm clearance so I finished to almost full depth with an 8mm cutter then a couple of finishing passes with a carbide 6mm cutter, which also gave some more definition to the transitions around the boss that sticks out. Then spot and peck drill the 4mm holes.
The plan was to hold them all upside down in the vise on the manual machine and cut off the supporting stock but when I took it out of the CNC machine vise it went banana shaped. Perhaps I'd used the BMS I bought for the slidebars. I compromised with it and cut it in half and two at a time seemed to sit well enough to go forward with the idea.
I decided to try spotting again given these are just clearance holes. I eyed the brackets into position as near to the middle of the top of the horn cheeks as I could and clamped them with a toolmakers clamp. This worked well.
I put two of them on tonight but that was enough for today. I did my actual job as well, and helped with #2 son's job, so this wasn't all I did!
I'll try that one day although I think the biggest free cutting bar I have is probably 10mm hex! That technique would have saved me the worry of cutting into the vise, for sure. And it was a bit worrying trying to work the stock off the back of the first pair wondering if they were going to fly out of the vise at the end.
I do like the Fusion 360 feature where you can define the operations to cut one piece and then say do another x of them at y spacing before generating the g-code. Plus you can tell it to do the same operation to all of them before changing tools. It makes things like this easy and I could do my real job with less interruptions than if I had to do 3 or 4 tool changes and part each one off as it was done.
I was pleased with the finish on the parts. It's better than it looks in the photos.
Hi David, I buy Steel bar in 5mm increments of size in whole lengths from my local Steel Stockholder, they cut them in half without charge so I can get them in the Smart Car. It's very cheap when you buy it like that. It's worth getting a 3 and 4 jaw chuck and adding a back plate to make fixing them to the machine table quick and convenient. It all takes time and money, but in the long run it makes life so much easier.
You're absolutely right about being able to make multiple features in one go. However, when you add in the time to separate and finish them afterwards, the benefits aren't anywhere near as great. I do occasionally make multiple parts, say from sheet, but if anything goes wrong it then becomes a bit of a nuisance. It takes very little time to swap the material or add an offset and run the program again.
The parts look excellent, and there's absolutely nothing wrong with the way you've gone about it. There's no right way, but it's interesting to explore the consequences of the choices we make when choosing a method.
Some more parts for the dummy leaf springs. I need another 2 of these, and 2 short ones that don't have the stepped part on them. They all need a 1/8" hole in the crown of the rounded end. I'll mill a little flat and use that to get the hole started. I don't have a 2 flute 3mm or 1/8" cutter.
I did some measurements and decided the hole centers in the frames for these parts were 9.8mm apart. I made a test piece out of 3mm steel with 6BA holes tapped in it at that spacing and it worked with the 4 pairs of holes I could get to without taking the front wheels off (they are on so the loco isn't sitting on the drain cocks).
This took 91 minutes with a 6mm carbide cutter. 1300rpm and 60mm/min feed, 1mm doc. The finish is quite bad compared to the last parts but they should clean up ok and you can't see them when they're in place inside the frames!
While it was being done I made the T pieces for the 0-4-0 tender.
That's worked out well. I think you're pushing the feedrate a bit on that, I'd be incline to reduce it to 30-40mm/min and add a bit of cutting oil to it. You'll be surprised at what it difference it makes if you give it more time to cut, and the tools will last longer.
More of the same, except two of them are shorter. I had less than 1mm grace on the stock so I was very careful in setting the X0 and making sure I wouldn't cut into the two already done on the left. If I couldn't fit everything on this piece I'd have had to buy a new length. The plus side of that would be I'd try to get 12L14 free machining rather than BMS . What is BMS actually meant for?
People more observant than me will notice there are no holes in the two on the left side. I've been doing so many things at once I just shut the machine down in relief when it stopped making noise and the dull cutter wasn't broken/hadn't torn the work out of the vise/didn't cut into the existing ones without thinking there were another two steps to go!
I didn't notice until I'd chewed the back off, broken the parts out, and went to chamfer the holes. Another demonstration that CNC doesn't take all the thinking out of the job :-\
Here they are super-glued to a couple that do have their holes so I can spot through.
All holes tapped and they do fit.
The short ones go on the second bolt down of the stretcher to the left. It has just occurred to me that I may need to thin them down and the hole in the top will need to be offset by the thickness of the angle - lucky I wrote this first!
The plan is to use that piece of 3mm strip one of them is screwed onto to hold them while drilling the hole in the top. If I can leave it in the vise then I should be able to do all of them without having to find the middle of each one. That strip was the initial test piece for the 9.8mm measurement.
Are you planning on having an inline clack between the lubricator and the cylinders?
Having found this blog via Roger's blowdown valve discussion I like the look of the design he used. I was also considering something similar to what is already there - the ball seating on an o-ring rather than a hard seat and see that Don Ashton has done this while reading his 9F thread this morning.
So there are a couple of options other than the usual ball-on-hard-seat which I wouldn't bother with because I know I couldn't make it steam-tight. But I'm going to see how it goes before I worry about an extra one.
Sorry I didn't recognise you - I looked at the username and thought you were someone else I 'know' from another forum who is building MSWJR stuff - the group of letters look the same at a glance. I didn't notice the location... that would have been a clue!
To put the holes in the top of the left spring backets I thought I was going to have to mill a flat and then use a spot drill and 1/8 drill to do it. Then the happy realisation came to me that I have a sharp 2 flute 1/8 endmill and a single plunge would do it with no tool changes! All went to plan and by using the piece of steel I'd drilled to prove the 9.8mm spacing of the holes I could just get one bracket in the right place and do all six of them without any more set-up. The two shorter brackets required a re-fixing of the X axis but that was all.
One of those jobs where it all went to plan as far as I can tell.
Hi David, Hopefully you got away with it this time, but I really wouldn't use any sort of flat bottomed cutter to drill a hole. That's because there's no self centering action and the hole will almost certainly end up over size. Spotting a flat, centre drilling, then drilling is much more reliable even though it's more work. Short cuts are rarely worth taking in my opinion.
I'll spare you the cock ups and wasted time and material and the various stupid things I tried and just show the finished result of a day in the workshop.
The entire day was spent trying to make and fit the two thin strips at the top of the cab sides. It didn't go well.
One easily avoided but difficult to work-around mistake was putting 1.6mm holes in the laser cut parts rather than the 1.2mm called for on the drawing. This means trying to spot 1.2mm holes through 1.6mm holes, in line, which for me isn't possible. When it's no harder to get something right and it causes so much hassle it's pretty upsetting.
The first side turned out just this side of acceptable, only because I hope it will be hard to see under the cab roof overhang. The strip on the second side is a write-off and has to be remade. It was superglued on and clamped at both ends and it still distorted while getting riveted on. I didn't notice in time to recover.
For now I've left the workshop and am pretty discouraged at how the first day of the year has gone in there. It's days like this when I don't understand people who say they find their time in the workshop fulfilling and relaxing! I like looking at bits I've finished but struggle to see how anyone actually enjoys the journey. As far as I'm concerned it was just a wasted day.
Keep at it David! Tomorrow will be a better day! Don’t forget we are all with you on the journey, some days are just “put down that tool, turn the lights off & close the door on the shop!” Take several deep breaths, head to the fridge grab a soothing ale , or what ever you prefers & plan for a better tomorrow!