Levelling Colly Student

[prepman]

For interest (or not).....Levelling is not a true term, but it's the one widely used for bed alignment.
Don't normally have an issue with producing accidental tapers (5 thou' ver 9"). But making an arbor for the Senior mill has been a bumpy journey, mainly by cutting corners.
On my Mk1 Student there are no headstock adjustments. The head unit was factory ground to give fit. The recommended action to settle the headstock down after calamitous event, is to slacken off the 5 socket screws and then re-tighten.
Have done this a number of times in the past with varying results. Anyway decided to check for bed twist. Used a white spirit filled test tube previously, but decided to use a laser level to see if it was a better way......It worked, but again not conclusive if the headstock is slightly
The story so far. Put centre in headstck and it spun true, so point is definiely centre. Attached the laser to the toolpost and aligned it vertically then traversed across to check horizontally aligned. Then ran the saddle to end of bed and rechecked/adjusted until centred at both points. Traversed out near headstock and marked laser on headstock, then from the end of the bed.. The theory is that any shift can only be due to twist, not even bed wear. I think I'm correct but don't mind being proved wrong. Obviously not vehemently.

 

[Pete.]

Do you have a sensitive level? If not send me a pm and I'll sort you one out.

 

[Agroshield]

...decided to use a laser level

It might be instructive to compare the manufacturer's quoted figures on the laser you are using (see: https://www.trend-uk.com/dlb-trend-digital-level-box-magnetic-angle-finder-uk-sale-only [0.2 degrees or 3.5mm per metre]) to that of a typical machine level (e.g. https://www.rdgtools.co.uk/acatalog...ivity-0.05mm-Graduations-8301-0010-10577.html [0.05mm per metre or 0.003 degrees]).

Going by those numbers, there is a factor of 200 difference between the two. Even if the level is grossly overpromising and the digibox is way underpromising, it would be hard to reconcile the two.

 

[Brad93]

Your laser line is no where near accurate enough to work to the level of precision you need.

As pete says you need an engineers/machinist level of at least 0.2mm/m or better.

 

[prepman]

Do you have a sensitive level? If not send me a pm and I'll sort you one out.

I used a diy one....good of you to offer. But I think the issue is elsewhere. Silk purse and sow's ear so to speak.

 

[prepman]

Ah....Just to explain.....I'm not using the laser level function at all. That would be pretty naff at best...it's trigonometry that's at play. You can calculate the deviation from the radius of the bar with sine. It all depends on if firstly the headstock is aligned. I know the bed is worn at the headstock end, just by the extra friction at tailstock end on the saddle. So I've got that to contend with and everything else is an added problem. Like I say from normal usage it isn't an issue, but machining shafts is another

 

[prepman]

Think the problem is resolved. Took the tooling off and mounted clock. It indicated a taper, which it shouldn't, it being on the toolpost. So it looks like it's spring issue. ie. the EN8D is harder at one end to the other, The soft end has had some welding and allowed to cool natural. The bar I assumed would be supplied annealed. But the cutting isn't even, with hard spots. So it's gone into the fiery furnace and up to 750C and left to cool over night.
The laser alignment is an acacdemic excercise, which IMHO should work?. Reworked the caphead screws and looked for deflection. None really, and only got 0.4mm to play with before it's undersized for 22mm arbor, it started as a 1" shaft from 1-1/4" stock. Slowly disappearing.
Thanks guys, especially @pete for the offer of a lendsy.
Next piece will be annealed first!

 

[Brad93]

More likely you're getting deviation in your tailstock than bed so worn it's making taper.

 

[prepman]

More likely you're getting deviation in your tailstock than bed so worn it's making taper.

Not using the tailstock....for very that very reason. So fine cuts it is...
However did a tailstock alignment years back and had to shim up. The overall alignment had been good, but whilst parting off I didn't catch the offcut which hit chuck and bed with resoundng crash, hence the concern for re-alignment. Tomorrow with the annealed shaft will tell if my theory holds.

 

[Brad93]

how long is your part?

 

[prepman]

how long is your part?

9" ..we are talking about the lathe?

 

[Brad93]

9" ..we are talking about the lathe?

9" at 25mm the part is deflecting

 

[prepman]

9" at 25mm the part is deflecting

I attempted it with the centre also and got same sort of results. Could put my travelling steady on but not really keen. If clock gauge says tapered it has to be flexing. But I think it's at toolpost spring also.

Storyline.....my Tom Senior Major mill didn't come with any horizontal mill components. So, I had to source a bar for the support beam and fabricate a bearing arm from 3 pieces of steel.
I also needed an 3MT arbor with dogs approx 300m total length. Availability was scant. so made everything.

The shaft is 2 pieces of EN8 one of 30mm job lot offcuts (another thread) and a 250mm length of 1" EN8 bright bar. Socketed and TIG'd together. This 30mm extra diameter was to create the drive dogs

That didn't work out as it didn't end up true and the 1" wasn't supplied straight either (bar end).

So attempted to machine it down to 22m to suit my involute cutters. Cutting keyway in lathe was doddle with toolpost drill adaptor.

Again I used the morse adaptor in the 3jaw.
Transferred to the mill and shaft wobbled. Eventually penny dropped and I used my Colchester nose 3MT adaptor and drawbar after removing chuck. This fixed the wobbly bit. Shaft ran true with no wobble.

 

[Brad93]

EN8 is never straight it needs straightening if you're going to use it in factory size.
I ordered a length from Acton bright, needed a shaft for a big ventilation fan, 54" long.
Nothing super high precision, it ran on pillow block bearings.
It was awful, had to press it to a few thou.

 

[Rrobson]

As Brad has suggested, 9x the diameter needs supporting if you want a true and parallel cut. You will fine that with a very sharp hss tool it will still deflect by a noticeable amount. Even if it is supported at either end it can still push the middle off.
If you are using carbide then light cuts can make it worse.

The problem you have is machining true. And en8 is hardly the most diametrically stable material. Just by machining the skin off you can cause the part to change shape. Then you’re also adding internal stresses by welding. You’d be better starting with one piece and machining in one go, or rough machining, welding then finish machining it all in one go between centres. That way the part will be held in an unrestrained position and shouldn’t change shape provided you keep the heat reasonable and consistent along its length.
Precision machine is difficult because everything has the ability to change something…

 

[prepman]

If you are using carbide then light cuts can make it worse.

Very true as they're designed for heavy fast cuts. It tapers towards headstock as if it's being pushed away at free end, so this morning I'll try the annealed bar. Maybe change HSS tool. See how it goes.
What I did after welding the 2 pieces together was to anneal it at 750C.
It's to replace the DIY MS arbors I've been using for years. Neither particularly good.

 

[prepman]

You’d be better starting with one piece and machining in one go, or rough machining, welding then finish machining it all in one go between centres.

That was my first abortive attempts....but due to parts not running true because I cut corners. Took 3 jaw off and using nose adaptor. Hate p'ing around changing chucks.

 

[Pete.]

Maximum hang-out is usually accepted as 6x diameter but for EN8 it's probably less. As it requires extra cutting force.

I was looking after some alignment tooling for a guy which was the stuff ZMT used sinuses for aligning hardings. Their headstock checking jig was a steel arbor about 50mm with two brass rings on it about set about 150mm apart. You skimmed the twp rings with a very sharp hss tool them measured them to check for taper.

 

[prepman]

Maximum hang-out is usually accepted as 6x diameter but for EN8 it's probably less. As it requires extra cutting force.

I was looking after some alignment tooling for a guy which was the stuff ZMT used sinuses for aligning hardings. Their headstock checking jig was a steel arbor about 50mm with two brass rings on it about set about 150mm apart. You skimmed the twp rings with a very sharp hss tool them measured them to check for taper.

For that I've got a 30mm test bar that I use, normally.... although fitting brass rings sounds a good idea. It's only that I had an incident parting off (didn't catch the offcut) that I suspected alignment issues.
Using the laser beam (not the level part) as an alternative to sensitive levels by triangulation, appealed to me, especially as I have the lathe sloping deliberately towards headstock for suds draining, to stop it collecting under saddle.
Yes EN8 is a pig of a stuff...although it's not as bad as some of the black stock I've got. Overnight annealing didn't gain me much. Fine cuts just burnished it...very shiney and then it digs in. However in the process I've realised that corner cutting doesn't work. As the mill horiz' uses a 3MT arbor, which I can machine easily enough. It was getting the remainder of the shaft running true to the 3MT. Trying to cheat backfired repeatedly. I might give up with the EN8 and remake an EN3 properly this time.
Finished this one off with keyway and arbor nut thread. But not satisfied yet again.
As to the taper...I used the tailstock and clocked it over to compensate...which worked until the tool bit in and took too much off....
Pee'd Off.....
Going to strim the grass instead or feed carrots to the horses,,,,

 

[Brad93]

Don't **** with en3 or en8 it's not what it used to be. Go straight to alloy steels like EN19/24.

Or have it ground.

@pressbrake1 has had lots of fun with long bars recently.