Member postings for Pete Rimmer

I have a few pairs of those left over, if anyone wants some. I don't advertise them because I never intended to do a production run but every so often they are unavailable so I keep some on the shelf.

The two are equal on a machine that is in well-kept or unworn condition. Where the prismatic way wins out is that it can suffer a lot of wear and still be in reasonably good alignment. Gravity does the job of keeping any looseness out of the assembly.

A flat bed way such as the Myford 7 uses will stil wear 'downwards' just like the prismatic one but any wear on the vertical shear translates directly into front/back clearance. This is why many flat bed lathes such as the 7 series and similar Atlas types tend to be loose towards the headstock and tight towards the tailstock - the tailstock end has little or no wear. This can also have an effect that doing any turning away from the chuck will give a drasticlly different cutting depth or level of finish than towards the chuck, something that the prismatic way machine will not suffer to such a great extent because again gravity is causing the saddle to sit down tight on the prisms.

You should not concentrate solely on the bedway in terms of evaluating wear for either types of lathe however. You will find that for any lathe which has significat wear on the bedway, the underside of the saddle will have suffered a much more significant amount. One of the best things you could do to a lathe which is showing signs of wear is remove the saddle, turn it over and scrape the underside ways flat then slightly hollow (less than half a thou, more like a couple of tenths). Saddles are nearly always worn more at the leading edges of travel whoich produces a boat-shaped underside prone to rocking and perfect for trapping grit which will accellerate wear further. Scraping them slightly 'hollow' will allow for oil retention under the saddle where you want it and will let them wear in before they wear out.

Edited By Pete Rimmer on 29/04/2023 12:05:21

Does the DRO report the correct position if you move the axis with the power off?

Vials might be ground of bent. The one in my box square is certainly ground as it works inverted.

I once made a belt in a pinch by grinding all of the ribs from poly-vee belt. I do believe that it is still fitted and working on that particular Mk1.

It all depends on the local TRO in force. It may, or may not exempt emergancy service vehicles (or it may only exempt them whilst responding to an actual emergency). Usually, unless the structures are in distress they are exempted.

This was an issue for Chertsey bridge IIRC where they imposed an18tonne weight restriction due to the bridge requiring strengthening work, but after the work was completed they kept the exemption in place to protect the bridge from damaging traffic but it didn't allow an exemption for emergency services.

No sweat I am often guity of the same. I get corrected more when posting whilst tired.

I actually keep two identical 4-jaw independant chucks on my rack one with the jaws set inside and the other with the jaws outside. It was the late John Stevenson who gave me the idea when he mentioned that he did this because swapping the camlock chuck was far quicker than reversing all of the jaws. He was of course, quite correct.

Course I've used one, they grip great for truly round stock but not better than a 3-jaw. Accuracy has nothing to do with number of jaws but quality of manufacture and state of wear. Same goes for gripping force for threading, 3-jaws are not reportedly poor for that because of some flaw in the design.

Where they fall over flt is on materials that is not truly round. Just like a 3-legged stool which sits stable on an imperfect floor where a 4-legged one will rock, the 4-jaw can allow stock to rock on 2 jaws where a 3-jaw will not.

As I said, if they did actually hold significant advantage they would be much more prevalent but they are not. You'll find perhaps one 4 jaw self centering for every couple of hundred 3-jaws.

You used a 4-jaw SELF CENTERING chuck for everything but holding a fly cutter?

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

If your part is less than about 3" across and you're anywhere near Kent Iain you could borrow my little furnace it'll hold 500degC to within about 10 degrees all day long.

Iain how about getting a thin sheet of titanium? That should blue up quite readily.

They must have progressed in the '80's as the 1979 Boxford drawing I have for cross-slide screws certainly specifies a blank dimension for thread rolling.

Edited By Pete Rimmer on 10/04/2023 08:41:46

We had one of those things and the same thing happened. The plastic sliders fell apart.

I 3d-printed some replacements from PLA. I have the files in .dae format and .gcode for a creality 3 printer, if you want them.

Edited By Pete Rimmer on 06/04/2023 19:43:51

Scotchbrite trapped in a twisted wire loop (I use 3.2mm aluminium tig rod), whizzed up in a battery drill will bring them up a treat.

No metal ball or roller bearing should be run dry. For a spindle bearing that is not oil fed, grease is fine. The pil on thebgrease does th lubricating, the 'soap's holds the oil. If you over-pack it then it will run hot just from the churning friction.

If you inspected the bearing and it has no grease at all, put some in ,but dont go crazy with it.

Paul, take a look here:

Mellor cross slide gear

The small gear is a circular pitch but you could make one with a mod 2 cutter I think and 2 degrees of helix. The exact helix you can calculate from the pitch and diameter of the screw at the rear of the bed.

This gear is almost always missing because the star wheel that engages it falls off, closely followed by the gear itself.

I wonder if anyone can find any instance of anyone ever being prosecuted or penalised in any way for using 'industrial' equipment on a domestic supply, in respect of the circumstances here? I suspect not.

Many industrial units only have a single phase supply no different to a domestic one.

Edited By Pete Rimmer on 16/03/2023 17:58:05

My expensive Licoln tig welder (~5k new) re-sets the digital clock on my workshop wall to 01:00 01/01/1999 sometimes and for some strange reason also causes it to play Greensleeves at the same time, due the the HF start. My £80 Lidl plasma never has.

So I'm with Mark Rand on this.