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9th Feb 2017, 12:38 PM #1australian metalworking hobbyist
- Join Date
- Jan 2009
- Location
- Holbrook, NSW
- Age
- 73
- Posts
- 490
sticky Hercus cross slides and compound slides
It has long been a problem, that as a machine ages the spindles and dovetails of the two slides can get out of parallel (generally only happens in extreme cases of wear). With the cross slide, the spindle is fixed in the saddle, so as the dovetails wear the position of the drive nut moves away from it's aligned position causing the nut to bind, particularly when it's all the way back to the dial end. The same principal applies to the compound slide. I had a play with one here and removed a small amount of material in the cross slide drive nut hole, to allow it a small amount of sideways movement, it went from being very hard to move to full length free movement again. What had prompted me to try this fix was the comments from a few owners about their machines becoming stiff after new parts had been added to a worn system. While the worn machines had play in the nut and spindle they could still move quite well but as soon as the new parts are fitted the wear in the slides causes them to bind.
Referring to original drawings it seems when the machines where originally made, as small amount of material was left under machined on the dovetail on the lefthand side of the saddle which I assume was done to allow a little extra life as the slide wears. This means the new machine was ever so slightly tight when new but freed up more and more as the slide was worn in. I think, when we remake these parts, a two piece saddle with an slide adjustable crank handle piece would solve the problem, allowing the screw to move with the slide wear and stay parallel. the same could be done with the compound.
Has anyone else tried this fix and what result did you get.
Sorry I can't post a pictorial representation as I gave my computer a cup of coffee and haven't got around to re-installing my cad and graphic software (when I find it) on the new computer as yet.
mal
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7th Mar 2017, 06:33 AM #2Most Valued Member
- Join Date
- Nov 2007
- Location
- melbourne australia
- Posts
- 3,228
Hi Mal,
As we discussed a few months ago, my new slotted cross-slide binds when wound fully back. I adjusted the gib screws and removed most of the binding. It also appears to be bedding-in.Chris
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7th Mar 2017, 03:12 PM #3australian metalworking hobbyist
- Join Date
- Jan 2009
- Location
- Holbrook, NSW
- Age
- 73
- Posts
- 490
Hi Chris,
Give me a call when you're at your machine, have a couple a ideas that should sort you out.
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13th Mar 2017, 08:20 PM #4Member: Blue and white apron brigade
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 7,183
Mine arrived today and I though it was sticky until i realised no it was just "not sloppy" like the old one.
A couple of winds back and forth and that bit feels like a new machine.
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30th May 2017, 01:58 PM #5australian metalworking hobbyist
- Join Date
- Jan 2009
- Location
- Holbrook, NSW
- Age
- 73
- Posts
- 490
I have been talking to people who refitted cross slide and compound nuts after regrinding and the most common approach seems to be machining out the mounting hole well oversize and pressing in a new piece. The hole is then rebored, in the new piece, to a new position to match the alignment of the new slide positions, thus restoring the correct offset of the drive nut to the fixed dovetail (lefthand side) and positions the nut correctly with the screw to give free movement over the full travel.
What happens when you take material of a horizontal surface of an existing dovetail or straighten a dovetail's sloping surface is in effect the top piece moves down and to the right. The downward movement can be compensated for with the drive nut being raised, so not a problem.
When I "eventually" remake the saddles, they will be a two piece part with the front piece, holding the drive screw, having a small amount of horizontal slotting to be able to be loosened and realigned with the drive nut and retightened. This will enable fully reground machines to be realigned without the need for additional machining.
Mal
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