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Thread: Hercus 260 Cross-slide play
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23rd Sep 2011, 07:13 PM #1Most Valued Member
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Hercus 260 Cross-slide play
Today I removed the badly mushroomed screws from my tool-post with the intention of facing and turning down the ends.
It turned out to be a humbling experience. I cut a slot in a couple of 5/16'' nuts , fitted them to one of the set screws and secured the lot in the 3 jaw chuck. I put a freshly sharpened HSS cutter in the tool-post, centred it and proceeded to make the cut. The vibration was terrible. I could see the whole saddle shaking. I tried lower and higher RPMs. That only changed the frequency of the vibration. I tried light and heavy cuts. That didn't help either. I fitted a different tool with a large radius on the tip. I was able to make a facing cut of sorts (it was actually a bevel because of the tool shape).
Once I broke through the case hardening the vibration went away and facing was fairly easy. My problem is I only want to remove the thread from the tip of the screws and the thread is the hardened bit!
There's a lot of play in my cross-slide. I can move the cross-slide 0.8mm by pushing and pulling on it (measured with dial indicator). To the eye it looks like a lot more than 0.8mm. I guess the nut is worn. Is this too much? Is it likely to be the source of my vibration?
I'm tearing my hair out. Appreciate any help.
Chris
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23rd Sep 2011, 08:53 PM #2Senior Member
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I had this difficulty until recently with my 9". Mal at Australian Metalworking Hobbyist has bronze nut spares at reasonable price. It's worth replacing the spindle nut in my view.
Mark
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23rd Sep 2011, 09:14 PM #3Most Valued Member
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Mark,
Thanks. Mal has them for $56. I guess I need one.
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23rd Sep 2011, 09:28 PM #4Cba
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First thing, you need to find out where the play comes from. It can be any or a combination of all of these:
- worn nut
- worn leadscrew
- too much axial play in leadscrew collar
Do you have a copy of the 260 maintenance manual? if so, there is a description on how to proceed on page 5. Otherwise use common sense, it is fairly simple design.
If nut or leadscrew are worn, you need new parts. Unfortunately the nut of this lathe has no adjustable slit to take out backlash caused by wear. If the nut is painted blue it is metric.
If the wear is on the leadscrew, it will be worse where the threads are used most. If the wear is on the nut, the play will be the same all along the leadscrew.
Some play is normal. Even a brand new Swiss made Schaublin lathe has about 0.1mm play. Otherwise the slide would be too stiff, and you would loose the all important tactile feedback for what your cutting tool is doing. With experience one can live with some substantial play, and still turn out highest precision results. But it is always nicer and more fun working with a slide that has no more than say 0.2mm play. Chris
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23rd Sep 2011, 09:46 PM #5Most Valued Member
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Chris,
my lathe has metric graduations on the cross slide collar, so I assume it has a metric nut. And it has serial number 20752, so it is a fairly late model. I'll remove the cross slide tomorrow and look for the blue paint to make sure.
I've got the maintenance manual with the explanation of how to remove the end play from the feed screws. If I'm reading it correctly I should replace the nut and/or screw first.
I'll check to see if the wear is in the nut or the screw. I would imagine that the bronze nut would wear much faster than the steel screw?
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23rd Sep 2011, 09:58 PM #6Most Valued Member
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I couldn't wait till tomorrow.
The nut is blue. The cross slide play is uniform across its full range of travel, so I guess it's the nut that's worn.
While pushing on the cross slide I noticed the front of the saddle moves up and down HEAPS. I suspect this may have accounted for the movement of the saddle I observed today. I'll investigate how to adjust this movement.
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23rd Sep 2011, 10:24 PM #7Woodworker/Metalworker
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If the saddle is moving up and down, check that the saddle lock bolt is not loose. The saddle lock is at the back of the apron and locks the apron to the underside of the bed track. If you have a parts catalogue, it's item 705.
If it's the cross slide that's moving up and down, check that the gib screws and/or the two bolts holding the cross slide swivel aren't loose.
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23rd Sep 2011, 10:27 PM #8Most Valued Member
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Thanks. It's not the cross slide moving up and down; it's definitely the saddle. I'll check the lock bolt as you suggest.
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23rd Sep 2011, 10:39 PM #9Woodworker/Metalworker
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Also forgot to mention, maybe check the two filister screws holding the cross slide to the apron. I've just completely dismantled my lathe, which I've only just bought, and the only way I could get up and down movement of the saddle was when I had removed the saddle gib on the opposite side to the apron, the two filister screws holding the saddle to the apron, and finally the lock bolt holding the saddle lock. If all these bolts are tight, I'm at a loss and would like to know what it is/was when you sort the problem.
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24th Sep 2011, 02:48 AM #10Most Valued Member
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If you mean that you can lift the sadle from the front,that is quite normal for these machines.
There are clearances with the 1/2 nuts,feed worm and rack and pinion.
The clearances on the 1/2 nuts and feed worm are either standard or slight wear.
If the clearance is excessive (maybe 3mm + or even a bit less) the rack can be shimed down to reduce clearance between it and the pinion.
Depending on how the fit of the cross slide nut is in the cross slide you may find it easier to replace the cross slide first and then insert the nut,there is no real reason to remove the cross slide to replace the nut,except for the purpose of cleaning.
If you wanted you could slot the nut and tap it and make a temporary adjustable cross feed nut.
I think he also has blank castings of the nut,this could be a good internal threading exercise.
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24th Sep 2011, 09:16 AM #11
If you are worrried about 0.8mm play in cross slide nut I think I am in serious trouble. I would use a ruler to measure mine if I was interested which I am not. I have some LH threaded rod and a nut on the way from US tho. Hope to improve things no end. One problem I have found is when trying to cut an acme thread (to make a new cross slide screw of course) the tool bit in and pulled the cross slide in with it. Given more experience it may be possible but the tool for cutting an acme thread is a lot of work to grind and if it gets damaged with each attempt it soon gets tedious. I changed my mind after the second dig in. I thought about using nylon clamped around screw like a split nut and attached to nut to prevent movement but have not got around to it yet and parts are on the way now.
Dean
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24th Sep 2011, 09:39 AM #12Cba
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Jack, you mention that your nut is bronze? The original nuts were made from cast iron. It means that your 260 has had the nut aready repaced at least once in the past. Possibly the prvious owner did make it himself (after all, that is what lathes are used for). Now if the nut wasby chance made from a very tough bearing material like aluminium bronze, it could well be that the leadscrew which (I think but not sure) is made from plain steel wears before the nut. Just something to think about.
Regarding the saddle, any play is very bad news. Check it is properly assembled with the apron and the rear gib strip. If there is play, it is usually only in a region close to the headstock, that is where most jobs are done on a lathe. Towards the tailstock a lathe is used much less, and wear is less. If that is your case, then the only remedy is to have the lathe bed reground (or, if it is only minor play and your lathe bed is not flame hardened, you could scrape the ways). Also check carefully the rear gib strip and how it is installed!
Another, much more freightening scenario, is that your lathe bed and the apron were cobbled together sometime in its past from two different lathes. At the factory, the saddle of Hercus lathes is selected and scraped to fit one only particular bed. Such a mixup could be a big can of worms, because how the saddle fits to the ways also determines the center line of the main (screwcutting) leadscrew to the half nuts and worm drive inside the apron. I could imagine it is not easy at all to get everything to line up in the end. But you mention elsewhere a 0.8mm gap, and that can impossibly be explained simply by wear, that sounds more like something seriously wrong like compenents mixed up from two different lathes, or another very major assembling mistake. Chris
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24th Sep 2011, 09:57 AM #13Cba
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[QUOTE=pipeclay;1378157]If you mean that you can lift the sadle from the front,that is quite normal for these machines.
[QUTE]
Pipeclay, I was at first deeply shocked when reading this. But...... you are right. I just ran out to my 260 to check. This lathe has indeed no guides to hold down the apron at the front. It relies entierly on the weight of the saddle and the cutting forces from the tool to stay down. And the saddle stop bracket, which I will in future aim to always keep lightly snugged-up!! This particular lathe design is full of surprizes. all other lathes that I know take great care at preventing the saddle from lifting off the ways, usually by adjustable gibs at the front. Now I understand much better, why with this type of lathe it is recommended to part off with a rear mounted inverted parting blade, it is because the saddle front can lift off but not the rear. Thanks for explaining this. Chris
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24th Sep 2011, 10:39 AM #14Most Valued Member
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pipeclay,
the front of the saddle probably moves up about 1mm (haven't measured). Certainly a lot less than the 3mm you mention. Mal rang me last night and said this is quite normal for a Hercus. Since the force when cutting is acting downwards on the front of the saddle it's not a problem. I guess it's only when the tool starts to bite, as mine did yesterday, that the saddle starts to jump up off the bed.
I'm not keen to try boring and threading my own nut from one of Mal's bronze blanks. I'll almost certainly stuff the job up and ruin a $56 blank. He hopes to have metric ones available soon. I'll wait till then.
Chris,
I only assumed the cross slide nut was bronze. You might be right- it may be cast iron. I'll have a closer look today.
I doubt this is a cobbled together lathe. There is no up/down or side-to-side movement in the cross slide. Only fore-aft (0.8mm). To me that can only mean wear in the lead-screw, nut and/or screw collar (i.e. the 3 sources you listed in post #4).
"One problem I have found is when trying to cut an acme thread (to make a new cross slide screw of course) the tool bit in and pulled the cross slide in with it."
Dean,
I reckon that's what was happening to me too. I gather the way to account for wear in the cross slide by backing the cross slide out and coming back in to make the cut. That obviously works when the cut is proceeding well. However if the tool digs in, then in my case, the saddle can move in as much as 0.8mm. The obvious answer I suppose is don't let the tool dig in. Easier said than done it seems.
Chris
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24th Sep 2011, 07:06 PM #15australian metalworking hobbyist
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bronze and cast spindle nuts
Hi Guys,
Sorry we haven't managed to supply the metric nuts at this stage, we are still in the process. When finished they will be available in both cast iron and bronze for about $56. For the intrepid d.i.y enthusiasts the blanks are available for $21 through the website in either material.
Excuse the advertising I don't normally subscribe to this but there seems a little confusion as to what the cost of things are. As for the play between saddle and way, it is the rear that is the important one which is why is has take up screws, play here should be at a minimum for free travel.
Mal
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