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Thread: Compound slide improvements?
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25th Nov 2021, 08:53 PM #1Diamond Member
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Compound slide improvements?
I have never been happy with the surface finish from my Hercus 9C.
It is OK on parallel turning Aluminium, but steel varies a lot.
As does facing off. Parting off is a crap shoot.
Ignoring the obvious, and hard to fix things for now
(badly worn bed Vs, cross slide dovetails and feed screw/nut),
I thought I would try to stabilise the tool post.
My compound slide casting is sad.
Missing a lot of casting, from years of school student abuse.
Which means there is a lot less surface for tool post to sit on/clamp onto.
In a perfect world, I would machine up a new one from a nice block of 4140 steel,
but who has the material, time, or motivation for that?
Time for some surface grinding. The frst thou removed showed a lot of wear in the middle, and on the mangled chuck side:
IMG_2216.jpg
Roughly another 5 thou off:
IMG_2223.jpg
and it's starting to get there.
That is all I dared to remove, because the T slot is modest, maybe 1/4" or 7/32" at the thin step?
So, I'll mount it back, and try some test cuts in steel, to see if there is any improvement.
Probably not, which means the next step would be to replace the compound with a solid block.
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26th Nov 2021, 06:28 AM #2Philomath in training
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You would be better off replacing it with a cast cross slide if replacement is the way you are going. Steel will 'ring' whereas cast will not so much. Unless you are using known steel that turns well, judging your lathe rigidity by surface finish is a bit dicey. The first thing I look at when I have poor surface finish is my tool grind/ tip.
My 2c worth
Michael
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26th Nov 2021, 08:12 AM #3Most Valued Member
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I think Nigel is better off replacing the compound with a solid block of steel as he suggested. The increase in rigidity is significant. Of course, the compound is still needed when angled cuts are required, so improvements there are still worth persuing.
If you don't have a slotted cross slide omit the cap crews.Chris
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26th Nov 2021, 06:42 PM #4Philomath in training
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26th Nov 2021, 07:26 PM #5Diamond Member
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It doesn't look like Mal has Hercus 9 compound parts, only Hercus 260,
and that would be many hundred dollars.
• Steel does ring. The experts say that either machining complex shapes (think webs, asymmetrical cavities), or attaching dampening (lead shot? granite epoxy mix), makes it similar to cast iron.
For shapes like the simple compound cross slide castings, not really an option. The thing has to be functional
• Steel theoretically dampens less than cast iron. If I'm reading this correctly:
Mechanical Properties of Gray Iron - Damping Capacity
Steel is between 20% and 400% worse than ductile iron.
(and Aluminium between 1000% and 4900% worse!)
Not sure what Hercus castings from the 1960s would be
• The larger the chunk of metal, the lower the resonant frequency (er, frequencies).
So, a steel compound that was 6" wide, instead of the 3" wide original, might be much better?
Anyway, jack620's suggestion might be my next step. I only have the standard cross slide, so its contact area is about 4" diameter. This was my design from a few months ago:
Hercus compound removal.jpg
However, I have some large cast iron slugs, that someone scrounged from the railways. Maybe 5" diameter, and 4" tall. That would be more solid - just machine a groove in the bottom, to clamp in with the two Hercus set screws, and a large thread in the top for a large cap head/socket screw.
But, before I jump in, some strategic dial indicators, and levering of the tool post is probably in order, because I'm not 100% sure the issue is in the compound slide. It might be the cross slide, or the carriage Vs, or the carriage gib up the back.
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26th Nov 2021, 07:47 PM #6Most Valued Member
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On a light lathe like a 9/260, I reckon it’s all of the above. But the compound will be the weakest link.
I have no data to back this up, but I reckon the improvement in rigidity gained from removing the compound from the equation dwarfs any difference likely to be found between cast iron and steel. But since you have cast iron slugs I reckon you should make your solid toolpost block from that.Chris
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26th Nov 2021, 10:46 PM #7Diamond Member
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Materials science, ringing, resonance, vibration damping
...In a perfect world, I would machine up a new one from a nice block of 4140 steel...
Diagnostic question: Do we think a tensile steel (like 4140) would "ring" more than mild steel?
My gut feeling is yes, but that is from playing with tensile shapes (like bolts).
I'm also wondering about the stress in a material - either machined or cast.
If it was normalised, or shot with little ball bearings,
would that cause less ringing?
I'm not a materials guy, and can't think how to search for that aspect
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27th Nov 2021, 01:05 AM #8
Hi Nigel, Guys,
I don't think that the ringing phenomena is worth worrying about for what you are doing !
Now in a boring bar that would be quite a different issue.Best Regards:
Baron J.
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27th Nov 2021, 06:55 AM #9Philomath in training
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Probably not. I can make a gear out of steel (any kind) that will ring like a bell. Out of CI and all I get is dull thunk when I hit it. All steel has the same Young's modulus, so has the same springiness. I think where CI really gets it's advantage from is the carbon in it's matrix which dampens the vibrations shuttling around inside the material. Shot peening etc will only affect the surface and the compressive stresses it generates are unlikely to increase dampening greatly.
As per John's thoughts, ringing is unlikely to have a great effect on things, especially when lined up against rigidity and tool geometry/ grind but even expensive machine tools are still made of CI so there must be some benefit.
Michael
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27th Nov 2021, 07:21 AM #10Senior Member
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Ringing (resonance / vibration) does affect surface finish.
Static stiffness and dynamic stiffness are both important.
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27th Nov 2021, 09:15 AM #11Most Valued Member
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27th Nov 2021, 09:16 AM #12Most Valued Member
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The 260 casting is around $130, knock the top off a bit if desired, you can still use it as is if wanted on your 9".
Another alternative would be to get a piece of suitable size cast round and make your own.
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23rd Dec 2021, 08:01 PM #13Diamond Member
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I agree, so I did some testing...
1) 400mm long, 14mm square bar in QCTP tool holder, with indicator on one side:
IMG_2312.jpg
and 15lb of weights on the other side:
IMG_2313.jpg
indicated about 5 thou twist relative to carriage/saddle.
2) Removed tool holder, re-tested against QCTP block:
IMG_2314.jpg
About 6 thou. Probably due to less-secure attachment of square bar.
3) Removed QCTP, but bar on top of compound:
IMG_2315.jpg IMG_2316.jpg
5 or 8 thou, depending on how badly I clamped/attached the bar
4) Remove compound slide completely. Had to bring cross slide back a little to attach bar:
IMG_2317.jpg
1.5 thou. That is more like it.
5) Now, reverse the steps. Make sure rotating flange on bottom of compound is totally clean, and re-attach. Then tighten the locking bolts tight. Very tight. And re-test:
IMG_2318.jpg IMG_2319.jpg
3 thou? Excellent.
So, .005" to .003" — I've improved it by 40%???
6) ... but because I'm a methodical kind of person, I think about how to improve it.
Cross slide seems to be 1.5 thou, compound the same.
I tighten the compound's gib screws, to the point where its slide is locked, and re-test:
IMG_2320.jpg
That seems to be 1 thou? No way. Cross slide was more than that.
So, I remove the weights, push the bar up and down a bit, re-zero, and put the weights back on:
IMG_2321.jpg
Closer to 1.5 thou, but I would expect a little more. Maybe 2.
7) Now, I'm really perplexed. I re-adjust the compound's gib, to the point where the compound slide can actually slide. Re-test. About 2.5 or 3 thou.
8) I now contemplate my testing setup. 15lbs is not a lot of force.
I decide to push down on the back of the bar. Hard.
Indicator goes up to 8 or 9 thou, then bounces back to 4 or 5. Take weights off, and back to 0.
Hmmm. It looks like the tightened gib has slipped.
That is enough testing for one day. I might try clamping the back of the compound, instead of tightening the gib, to see if that gets me back to 1 or 2 thou.
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23rd Dec 2021, 08:38 PM #14
Hi Nigel, Guys,
Your testing and the results are interesting !
Any sliding joint will exhibit some play and each will add up, in particular gib strips will move even if pinned. Then there is the oil film, the oil will move out of the way any time there is pressure. So there will be microscopic bumps where the adjusting screws have caused the oil to move out of the way.Best Regards:
Baron J.
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31st Jan 2022, 07:37 PM #15Diamond Member
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The tighter compound slide seems to give a better result, but I am still thinking through options.
A rigid compound replacement still appeals, and there are some nice ELS devices out there:
ELS4Basic_front_1200x12001.jpgELS4Pro-frontal_1200x1200.jpg
that can control both axes (i.e. do tapers, machine ball ends, et c.)
https://www.rocketronics.de/shop/en/...w-els4pro.html
Took the cross slide off today to clean:
IMG_2438.jpg IMG_2439.jpg IMG_2440.jpg IMG_2442.jpg
For fun, I have been looking online at left-hand ball screws. The cheap ones have between 2 and 10 thou backlash. A quick and nasty test of mine, by locking the slide with a clamp, shows about 7 or 8 thou on the screw:
IMG_2443.jpg
That is obviously only at one place on the screw.
A dial indicator might show a different result, but in today's heat I couldn't be bothered setting it up, and pushing/pulling the slide.
Basically, not really worth the effort to buy/machine either a new nut, or to try and fit a ball screw?
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