My first thought looking at the photos is that your grooving tool has a lot of stickout.

If your saddle isn’t in contact with the bed properly I suspect there is a

potential for “bounce” for want of a better description – the saddle dips as the cut comes on, then as the chip peels it lifts, changing the tool angle, which causes it to dip again….

Can you add ball bearing gibs like on a 10ee to the back of the saddle?
Dave

I could see the original plate on WM250 bending when parting off or making heavy cuts. I replaced it with a 15mm thick plate, using all of the original topslide fittings and four M6 t-nuts. The original plate needed to be done up really tightly for any clamping effect. The new one just needs the four bolts to be nipped up with a 10mm spanner for much better clamping.

The new plate was hacked out a larger chunk with an angle grinder, the cut edges filed smooth, and the mounting/clamping faces machined in the lathe. I keep promising myself I'll paint it, but that's unlikely to happen until I paint something yellow….

I can't imagine using 1" tools on such a small machine, and definitely wouldn't want to pay for them. Most of mine are 8mm shanks, used in a Myford size Dickson QCTP, and they're not the limiting factor.

Insert blades have a propensity to chatter unless the feed per rev is above a minimum value. I use inserts for parting off with a minimum feedrate of 4 thou per rev. But for grooving I grind a HSS tool bit which will give a better finish and no chatter even when sneaking up on a dimension.

Andrew

Worth trying a shorter grooving tool, easy & cheap. I found on my Myford super 7 the revs had to be way down low to stop chatter like this.

Tony

For parting on my Boxford I made a very stiff system and for my 250 with solid flange another.

The ME photo insert system is a disater waiting to happen for us unpaid writers

Edited By Niels Abildgaard on 18/03/2021 10:52:13

If people are looking for 'stiffness' in their tooling systems why do some many have a tendency to use round tool towers etc when square would be so much better?

Tony

The undersides of the bed front and rear are bearing sufaces for the keep strips that constrain the saddle vertically. These faces should be machined parallel to the top bed formation to a similar standard of finish. The keep strips can be solid blocks, ground or scraped to be in running contact with the bed when bolted up tight, or a bolted on piece designed to hold a tapered gib strip for easier adjustability. The saddle should not be able to lift regardless of how the load is applied – adding weight to the saddle to keep it in contact with the bed is not the right way to address the lift issue. IMO correctly adjusted saddle keep strips are an essential part of the machine.

Changing to linear bearings would probably make the situation worse rather than better – they make for very "lively" axes where what you want is better damping.

The bed design on these doesn't seem too good if it is similar to the model Nils shows – in one of his other posts Nils showed one of these machines stripped down & I was struck by how poorly the headstock is supported due to the amount of metal removed underneath it to make space for the motor. Most Western lathes continue the bed at it's full form (or beef it up) under the headstock to properly support it.

If I was to add weight it would be in the form of a substantial flywheel mounted at the rear of the spindle.

Tool overhang, cut width, toolpost footprint, direct drive variable speed spindle drive shortcomings & the requirement for a solid foundation have already been mentioned above. I would also look at adding non-drive end support bearings to the ballscrews & really the Z axis arrangement is "the wrong way round" – the motor & end support bearing bracket would normally be positioned where the feed gearbox is, so that the ballscrew is in tension when under normal cutting loads & so not subject to buckling, with a support bearing at the tailstock end. On a screw of that length, I would have a bearing arrangement that allowed the screw to be tensioned rather than just a single deep groove ball race support. Hiwin Ballscrews application notes give details of how ballscrew performance is affected by support bearing arrangements – a copy can be found as a .pdf on line.

If it is any consolation, even large industrial lathes can struggle with grooving. At my last employment we sold a straight bed Boehringer CNC lathe to an aerospace company & I was sent over to investigate when they complained about chatter when grooving. The machine was (IIRC) 800mm swing x 4 meters between centres, 22Kw drive with 4 gear ranges & probably weighed in at around 16 tonnes, but it chattered when the customer attempted to use an 8mm wide grooving tool. Tried all sorts of mechanical adjustments, control and drive settings but to no avail. Cutting the groove with a 4mm wide tool was chatter free, but the customer was adamant that the part had to be made with the 8mm item & the machine, in the end, just could not do it.

Nigel B.

He also has a very nice home made epoxy granite CNC mill, have a look at his "Elke" videos. Youtube's subtitles are not too bad.

J

PS Should not be long until you can like the new software!

Edited By JasonB on 18/03/2021 14:47:55

Thanks for the clarification Nils.

The lowest photo is the one I was thinking of – light use only there, I think !

Nigel B.

Yes when you see inside the headstock, it does not look overly massive. The word Gibraltar certainly does not come to mind.

It's hard to tell from the pics, but it looks like yours has the common shortcoming of many Chinese lathes: The bed width is narrow in comparison to the spindle height. It looks like the bed width is quite a bit less than the spindle height. So the triangle between the bed shears and the spindle is a tall, narrow based one. That's inherently less stable than many better quality industrial lathes and toolroom lathes that have the bed considerably wider than the distance from bed to spindle, so they have a flattish, broad-based triangle to spread cutting forces over. So between the headstock bulk and the bed wiidth, you are never going to get the type of rigidity you are used to in industry.

But as you've seen, going through and "blueprinting" the machine should tighten it up considerably.

I wouild not go with springs under those saddle lift plates. Cutting forces will overcome those springs. Best to do like Myford and most others and machine either the lift plates or the area where they mount on the bottom of the saddle so strips of shim can be used to get the desired half a thou or so clearance there. Anyway, if yoiu are plunging straight in you should have the carriage locked, which ideally should lock on that rear bed way. Might be an addition to consider if it does not have one.

I know you like that 1" tool and the overhang would be fine on a big rigid industrial machine but is just begging for trouble on these smaller flimsier machines.

If you go through as you are and eliminate all these little things, the sum total should put you ahead of where you were. But you are not going to make a Monarch 10EE out it due to the core design and build factors.