Binding on axis when locking off other

I was just wondering if anyone could shed any light on a problem I’d been having on my SX4 please? I’ve only used it for about 30-40 hours since I bought it last year and Id like to try and get cutting again soon but I’d really like to remedy this first as it made using the machine harder than I think it should have been.

What I was finding is that if I locked off the cross axis (the X axis that runs left to right as you’re stood looking at the front of the machine) then the Y axis (in and out) would become really quite stiff to move with the handle -needing two hands over longer cuts.

I couldn’t figure out for the life of me how locking one axis would cause binding on another. I’d be grateful for any advice.

Regards,

Matthew

Could be distortion of the worktable? I have seen, on these lightly constructed machines, work clamped to the table causing the movement to become somewhat stiffer due to distortion.

What to do about it I don't know.

John

The saddles on these things are very low profile and seem to get thinner and thinner in terms of meat on their bones, I wouldn't be overly surprised if you tightening the two front screws to lock the x axis is causing the Y ways to bow slightly.

Just to clarify, i think the weakest point of the saddle will run right to left where the cutout is for the X screw, I seem to recall it gets down to sort of 1/4" steel thickness which means load is transferred across the thicker Y dovetails below.

Next question.... how tight is tight? I only nip mine, a good squeeze with a screwdriver sort of tightness, I wouldn't use an allen key or spanner to gain any leverage.

Edited By Russ B on 05/06/2019 11:46:12

I've always had the same problem on my RF-45 clone. Perhaps because I only tighten up the right-hand screw on the X axis or the front screw on the Y axis the table skews and the non-locked dovetails are rubbing.

Well I went out and tightened the X lock on bot the X3 and SX2.7 as hard a sI could last night and the Y-axis moved as freely as it did with them unlocked so I can't really see it being flex as the SX4 is a meatier machine.

One thing to watch is that you don't have the end of a locking lever hitting another part of the machine, the SX2.7 can do that if the loose lever is hanging down and you wind the table right back towards you when things will seem to go tight but infact the lever is being bent.

Also on the subject of bending things make sure the chuck gaurd is not hitting a hold down clamp or vice, can have the feel of a tightening leadscrew as you merrily keep winding it further into the fixed object. Again teh SX2.7 is prone to this and your SX4 has the same gaurd arrangement unlike the X3 where it is height adjustable.

Is the saddle thicker on older machines? I'd seen some photos online which seemed to show some meatier than others, but I couldn't tell if it was age,model or rebrand specific etc

It may be worth examining the casting closely when the lock are applied, maybe a casting has been cracked and is distorting when the locks are applied.

Mike

Hi All,

Thank you for all your replies. Sorry I've not replied sooner - I somehow didn't subscribe to my own thread!

Frances - It was locked in just the one axis. You're right though, it did seem strange to get used to which lock locked which axis.

I couldn't see anything that could cause it to lock either. It didn't make sense that these locks could affect both axes.

John - With the locks tightened (and not touched) it does seem harder to move the axis when the table is closest to me, and eases off as it moves away, so I suspect there is some slight distortion.

Russ - I understand what you're saying and it makes a lot of sense but if Jason doesn't find the problem on the X3 it makes me wonder.

Jason - Yeah I've caught one of the locks on more than one occasion! When I tested the table again just now theres nothing to foul the movement and the head/spindle and chuck guard are well up.

Unlocked, the axis moves lightly and the difficulty in moving Y gets harder the more I tighten them. Tightening just over screwdriver-tight as Russ suggested helped.

Mike - This would be dissapointing as I only bought the machine last summer. When I tighten the locks, where might I be look for a crack? (along the length of the table or on the base of the machine/ways along which the Y travels?)

Matthew

I've been and had another 15 minutes winding the table in and out.

One thing that might be worth mentioning is that there's a gradual darkening to the oil I'm applying to the machine - I wonder if the saddle is flexing and effectively re-scraping the ways? Over time this might result in an easing of moving the axis (the saddle must get to a deflection and not go any further I'd imagine, surely?).

That's assuming there isn't a crack like Mike said - but I can't see one. I've uploaded some pictures in case anyone else can see anything from them (Russ - does this look like a thicker or thinner saddle to you?)

Wasn't sure whether a link to the album or the individual photos is best practice so I've included both:

**LINK**

An observation I've made is this:

1. Table in the middle of Y-ways. Lock the X axis. Move towards me (along Y). Gets VERY stiff in the last 2-3inches of travel.

2. Table closest me on the Y-ways. Lock the X axis (same force). Move table away from me (along Y). Table is easier to move in the same 2-3 inches and eases up towards the middle of Y-ways.  Feels like I'm going downhill!

As the table gets easier to move (as it's moved towards the middle in 2.), it seems like it's easier to overcome the locks when I try to forcefully move X - compared to when the table is closest to me in that 2-3 inches.

And when the table is stiffer (like in 1. when I've moved it into in that 2-3 inch range) it seems harder to overcome the locks by forcefully moving X.

I hope that makes sense!

Matthew

Edited By Matthew Sugden on 07/06/2019 22:54:59

Have you tried the x locks one at a time to see if one has a bigger effect than the other.

Although it will mess up your settings what if you tighten the table by tightening up the gib but check the procedure as one end screw is presumably a lock and you don't want the adjusting screw to be pulling too hard on the cast iron gib slot. This would distribute the stress away from the point load of the locking screws.

Is it possible to release the y axis nut? Sometimes slides get stiff as they approach the handwheel end if the screw and nut are not perfectly aligned though this shouldn't be affected by the x axis. (clutching at straws)

Is the feedscrew for the Y-axis movement absolutely parallel to the slideways? This can cause binding at the end nearest the handle.

This may be adjusted by loosening the plate that attaches the feed handle/screw to the table when the table is wound fully towards the handle.

Andrew

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This is easy to do on my similar mill and I've damaged my right hand lever by doing so. Although the lever is only slightly bent, on the inside something is wrong - the lock comes loose and needs regular readjustment with a screw-driver. As it's a minor inconvenience, I've not bothered fixing it.

I wonder if Matthew has a more serious version of the same problem; perhaps forcing the table with two hands broke the locking mechanism and/or displaced something inside. Try unscrewing the locking bolt completely and looking for damage; on the bolt and whatever you can see by looking down the hole.

Unfortunately the suggestion doesn't explain the symptoms unless the table itself was damaged. You might have to dismantle the table completely to see what's causing it to stick. It's a very odd problem.

Dave

Edited By SillyOldDuffer on 08/06/2019 10:19:27

Barrie, the slotted screw is one of the two push/pull screws on each axis to adjust the tapered gibs

There does not look to be a lot of oil on those ways, left hand of the Y axis does not seem to have much and undersides of the two X ways don't either, certainly no sighs of excess oil having run down the casting. Also what oil are you using?

Edited By JasonB on 08/06/2019 13:14:43

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Dear Matthew, I have read somewhere that tapered jib strips can distort causing the adjusting screws to disengage or try to bye-pass the tongues in the jib strip. Reworking /replacing the jib strips solved the problem and from memory the symptoms were the same.

Robert Butler

Thank you all for your feedback again!

Bazyle - Yeah I tried that and neither seemed particularly worse than the other. The locking-effect seemed cumulative and proportional to the additional stiffness.

Andrew - I can only infer the Y-axis feedscrew is parallel because there's no binding when the X-axis locks aren't tightened (I'm not sure how to accurately measure the perpendicularity of the screw). I would expect binding all the time if it was a screw-related issue. I did try adjusting the feed handle's nut last year and it did make a difference to the overall tightness and also seemed to affect the backlash. I think it's in a position of reasonable compromise at the moment for general use, it's just the additional tightness from the X-axis locks that's been a problem.

Barrie - Thank you, I do think it has to be flex in the machine and possibly over-tightening of the locks. Before late last year I hadn't milled since Uni and used some Bridgeport-looking machines where things stayed where they were put. I guess even on the SX4 it's all about reducing the cutting forces to within the machines ability (had an issue with up-cutters being pulled out of the ER collet while trying to cut slots last year because I couldn't get enough clamping force on them vs the force from the cut I was making).

Dave - I think I see what you're saying but I think the handle of the lock bent more than the screw so I'd expect minimal damage on the inside. I've had the locking screws out and they seem OK. (they're such a bad design for where they're placed)

Jason - I am beginning to suspect a lack of oil has certainly exacerbated the problem! I had been applying oil directly to the ways because I'd not realised those ball bearings were oil-points.

Is there any chance that the gibs are slightly different thicknesses? One of the locking screws goes in further than the other. I'm using Fuchs Renolin CLP 68 Gear Oil on the ways. It's some I bought to use on my CNC routers linear rails and ballscrew (but I'm now wondering if it's a little too thin for something as slow-moving as a milling machine?).

Robert - I should probably take a look at the jibs as they've been mentioned a few times (and one locking screw goes in further than the other) but being so new to milling I was concerned about re-setting up the machine afterwards.

Matthew