never had any success with parting tools - sooner or later they always seem to dig in and cause the whole machine to come to a violent stop.
the current lathe is a colchester student, which has power crossfeed, so I can eliminate ham-fistedness on the feed wheel in this case.
It does however have a small amount of play in the cross feed drive, such that the top slide will move slightly on the saddle. It occurred to me that when driving the topslide forwards, the topslide can move of it's own volition, further forwards, IYSWIM, and this might be the reason. The other lathe, which is currently undergoing renovation, has the same problem with it's cross feed, although it's not powered.
On or around Wed, 11 Jan 2006 10:01:21 +0000, Austin Shackles enlightened us thusly:
should say that this is probably the nut under the cross-slide, not the drive system itself.
Further experiment appears to show that if I lean on the toolpost so that the drive is holding it back, in other words, so that it can't move forward on its own, it appears to work OK.
So, next question... how does the cross-slide come apart and how to I remove the play in it? Is it adjustable?
You're not worried about the right thing. Most (manual) machines have backlash---a necessary evil, particularly if they're old and well used. The problem is that the wear doesn't occur uniformly, so unless you have a loaded nut, if you can eliminate the lash where it's the greatest, you won't be able to propel the cross slide where there's less wear, because the nut will be too tight. That means you're going to have to tolerate a given amount of lash----or invest in some serious machine rebuilding.
What you should do is concentrate on tightening the gib instead. You'll be facing the same problems with wear, but there may be a magical point where it's snug enough to eliminate the machine pulling your tool in. If not, you may simply have to live with the condition, or do the above mentioned rebuilding.
You can help yourself considerably by keeping everything as snug as possible, and making sure you have everything in your setup as short and rigid as possible. If the cut is causing the parting tool to dip under cutting pressure, that may be your problem. Keep the compound rest either locked, or keep the gib so tight you can't move the compound. It usually takes only a couple seconds to back off the gib if you need the compound. It's also a good idea to keep the compound back on the slide, so there's little, or no over hang.
You using a lantern (rocker) toolpost? Lots of positive rake on the parting tool? That in itself can be in invitation to trouble. How much front relief are you grinding on your parting tool? Too much? That's a mistake. Keep it to a minimum, so it helps control feed----that's what it's intended to do, and the cutting edge will stand up all the better, anyway. Are you running your parting tool on center? If not, why not? The moment you go below, the forces start pulling the tool in instead of bearing down.
Check out a few of these things and get back to us.
On or around Wed, 11 Jan 2006 10:18:39 -0800, "Harold and Susan Vordos" enlightened us thusly:
well, yeah. But I suspect it's worn such that there's play throughout the range of travel - I'd investigate, obviously, and if it is possible to adjust it then it can only be adjusted at the tightest point, so there'll still be a bit of play somewhere.
Gib might stand a bit of tightening, I'll have a look.
it is already not overhanging, although tightening it for parting-off is a good idea.
4-way quick-change thing, seems quite solid when locked in place.
near enough on centre. The points about relief and so forth I'll look into
- it might bear regrinding a different shape, at that. It's as it came, at the moment, so whatever shape the previous owner ground on it... I'll give it a go with less rake and relief, see what happens.
Front relief, no more than maybe 6 degrees. Top rake, no more than 8 degrees, and all the better if it is a gentle radius, wheel diameter, for example. By limiting these, it should require slightly more cutting pressure, which will reduce chatter and prevent or minimize hogging.
Hi Austin, Make yourself another toolpost and mount it on the rear of your cross slide, fit your parting off tool upside down and approach your job from the rear, you will be parting off 3" bar in no time with no tool grab. Regards Rotty ( Tamworth )
Lock the saddle down. - engage the lead screw with it in stop or use a way stop. On mills, a Gib would be locked and then movement is limited.
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Aust> never had any success with parting tools - sooner or later they always seem
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