Author Topic: Machine Mod 2 - Myford to ER32  (Read 6306 times)

Bogstandard

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Machine Mod 2 - Myford to ER32
« on: January 29, 2013, 04:34:33 PM »
Here is the second transfer post that I hope will show people that you are not stuck with what you have purchased. With a little thought and planning, you can fairly easily get machines to accept tooling between each other.

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This won't be a warts and all post like usual, just a quick skim thru showing some items that haven't been seen before.

This has been shown on here before by Arnold, but he tended not to show how a few things were done.

First off, I got a lump of the tough hydraulic ram material. If I knew the problems that this was going to cause later, I would have used another material.
I measured up the hole at the bottom of the ER32 holder, and that size was bored thru this piece.



I took the internal diameter measurement of a commercially made Myford part.



And the depth as well



These were the sizes bored into the back of the piece part.



I also bored a runout on the far side of where the threads are to go, to allow the threading cutter to have a safe run into area.



The toolpost was offset half the thread angle (55 degs), in this case 27.5 degrees, the opposite way to a normal external offset thread cut.
By doing it this way, when you put your cut on with the topslide (coming towards you) the tool is cutting on it's forwards face, just like you would do using this method for external cutting.
Everyone uses the method they feel the most happy with, some cut from the inside coming out with the tool upside down, others use just straight plunge cutting, this is the way I do it, and it works for me.



Then the tool was set to perfect height, and squared up to the job.



The saddle stop was set up, but it would slide if needed, at the max cut length.



The tool was marked up with the width of the runout, from the end of the thread to the back of the runout. If I stopped the cut as soon as the mark started entering the hole, the tool would never reach the back, even though the tool is actually moving forwards as you set each cut.



This was where I hit major problems with the material.
I thought I would finish off the last couple of thou depth of cut with the cheapo taps I had bought. These taps would be great for free cutting mild steel, but not the stuff I was using here.
I managed to finish off the threads with them, but it was very hard work.



This is a piccy of the threads. They look absolutely awful, but in real life they are perfect. I think it is a combination of oil and flash photgraphy that made them look so bad.



The part fitted perfectly onto my Myford nose adaptor, and it was turned up ready to have the external metric threads cut.



The threads are 1.5mm pitch, and this is the first metric thread I have cut on this machine since I purchased it over a year ago. Everything went very smoothly.



I had purchased a ball raced nose nut specifically for this job, and it screwed on and fitted perfectly



Now we get to the tricky bit, cutting the taper for the collets to fit into.
The standard taper for an ER collet is 16 degrees inclusive, so that means the topslide (compound) needs to be set over by 8 degrees.
This was duly done, but you have to remember that the taper is critical for correct operation, and this is only a very rough setting. A little later, things are tweaked to get the taper exact.



This shot shows what the setup looks like.
The topslide is set over, a boring bar is in the toolpost, set as though it would be boring a normal hole, and the saddle locked up.
All cutting is done using the topslide feed handle, so you need to get your technique sorted, whereby you use both hands in a swapover motion so that you get a steady and constant feed with no 'jerkiness' between changeover. This ensures you have a nice smooth surface for the collets to slide on.



I cut about 2/3rds of the required meat removal and then blued up the internal surface with Engineers blue, NOT layout blue. Engineers blue doesn't set and go dry, and so can transfer itself onto anything it comes into contact with. I usually have to give the whole area a good clean down afterwards, as the stuff seems to jump from here to there all by itself.



Taking the smallest and largest collets from the set (to allow for the different springiness) the collets were gently pushed into the blued up hole and even more gently, rotated. You want to make sure that your actions don't compress the collet at all, otherwise you may get a false reading. That was the reason for using the two collets, just to make sure I wasn't pressing in too hard and I was getting a consistent result.
The two lines at the tops of the collets are the top one is how far it goes into a normal collet chuck, and the bottom, how far they penetrated into the taper I had cut.
As you can see, the blue has only transferred onto the bottom part of the collet tapered face. This shows me that the angle that I am cutting is too large.
I slackened off the topslide bolts very gently, and tapped the topslide with the plastic end of a small screwdriver to reduce the angle by a minute amount.
Things were tightened up again, and a skimming cut done so that the old taper was only just cleaned up. You don't have a lot to play with, so while you are fine tuning, you take off the minimum material to do the job. I found the sweet spot first time, you might take a couple of 'taps' to get it spot on.
The new taper was blued up and rechecked again with cleaned down collets.



This is the result of my 'adjustment'. I have blue showing from top to bottom of the taper. The uneveness is caused by the rough finish on the taper, but as long as it is as shown, then the finish will be tidied up at the final stage. I have my taper now spot on.



The next stage is to get the taper to the correct diameter. So after the collets were cleaned up with spirits, they were place in my normal chuck and the depth marking was put on. This shows how much deeper it still needs to go. It looks a lot, but when dealing with tapers like this, even a tiny skim is a lot.
When I got to the final skim, I really slowed down the hand feed, and speeded up the chuck.



I was considering breaking out the toolpost grinder for a final lick over, but the results I got by hand feeding will be just fine.



The collet now sat at the correct depth.



So now the moment of truth.
I grabbed a 16mm collet and a new tungsten cutter, and by mounting the cutter in the wrong way around, I had a reasonably accurate test bar.

A quick check with a high precision DTI showed I had a TIR of 0.0001".

A fly farting as it went past could have caused that, so that'll do me.



So onto the mill, and using the newly made RT adapter and a woodruff cutter, I made some slots for the C spanner to fit into, just so I can get the thing off wherever it is mounted onto. I actually had to chisel it off the lathe fitting, but the first cut with the woodruff took the gouge mark out.



I can now interchange either 3 and 4 jaw self centring chucks, an ER32 collet chuck or a small faceplate between my lathe and the RT on my mill.



The next bit soon


John