square top Colch / Student

Frank in France,

Good morning out there.....Help please.....

1 I need to adjust the cross slide nut's (to much free play) on the above machine, looked in the parts book but not much help....any idea's.......

2 I'm just fed up with the original 3 jaw chuck, (only holds on the back of the jaw's) would like a new one.....I'm scared of buying without a recomend and all this talk of getting a duffer after spending loads. So can anyone recomend a make and if they make something accurate....I don't mind where in the world it come's from and price is not everything but as a hobbyist I can't afford a £1000 for a six jaw.....a good used one would be OK its just got to be accurate as poss.....

I know perhaps I should get used to a 4 jaw but I'm not that fast at alignment as I'm always in a rush for something.....

many thanks Frank

Hi Frank,

can't help you with the corss slide nut, but if the jaws of your 3-jaw is worn you could grind them.

Here's a video, and here is a description. Remember that even a new self centering 3-jaw will have some runout.

A Bison chuck should probably be Ok for your use.

Thor

Not sure if there is any adjustment in the nut but think the free play in the spindle to cross slide can be dialled out/adjusted if there is any free play there.

As for the chuck, as Thor said grinding the jaws should bring them back to square, it is an idea if not already done is mark the chuck to spindle position so that if it is removed it goes back in the same place.

As far as a new chuck is concerned there are a few options here **LINK** with 3-D1 fitting. Not sure of the size you are looking at also if you want standard accuracy or something better. Pratt Burnerd chucks are similar in price to Bison but the choice is yours both are better made than lower cost far eastern options.

Bob

P.S. Thor, thanks for the second link, it was the way to true the jaws that I could not quite remember and does not require machining of the jaws, I seem to recall a similar method in ME or MEW from the late 60's but could not remember just how it was done.

Edited By Bob Brown 1 on 29/05/2014 09:04:36

Grinding the existing chuck jaws will transform your chuck but if you do not have a toolpost grinder there is another way.

Purists might be offended but I have trued up chucks (including Jacobs type drill chucks) using just an oilstone. (the diamond coated 'stones and files are even better for the purpose). With a little patience you can correct for eccentricity and squareness.

You need a test piece (good quality unscored drill shank) and a bright light. With the light behind the chuck you can see where the jaws make contact and stone off the high points on each jaw until you get full line contact. To get the best results the process is iterative in that (with a worn chuck) the jaws might 'tilt' so consistency will rely on all three jaws applying pressure equally.

Use a DTI to determine to which jaws need adjusting for length, also if you have a longer test bar you can check run out at different distances from the chuck and fine tune the squareness. A felt tip marker and notepad are useful so you can make notes and marks and grind more than one surface whilst the jaws are out.

Ian P

Ian,

Not a purist but a practicalist (is it a word?). If I had to true up a chuck your method is far superior as you are actually checking the jaws when fully tightened.

A toolpost grinder will only cut metal when the chuck is empty and the jaw can flop anywhere.

Trevor

Ian,

The idea/method involves tightening the jaws onto something - either a ring inside leaving the bulk of the jaw free to work on or a ring outside the jaws with them pulling out to take up the slack. It is the same as boring soft jaws.

Mark

Trevor

"A toolpost grinder will only cut metal when the chuck is empty and the jaw can flop anywhere."

If you look at Thor's links like this one http://www.homemetalshopclub.org/news/aug04/aug04.html  then you will see the jaws have been tightened before they are ground such that they are not flopping about and should with a little care give good results.

Bob

Edited By Bob Brown 1 on 29/05/2014 13:12:34

Edited By Bob Brown 1 on 29/05/2014 13:13:09

I have a colchester with the same problem, but i use the four jaw chuck much more anyway, it supports the work much better and you become very quick at setting the work up concentric with a dial gauge.

'Very quick' is relative expression! I recently cleaned up the head of a batch of 100 bolts and would not consider using a 4 jaw for that type of work.

I use the 4 jaw when I need to do a second operation or hold something irregular but I would not want it as my everyday chuck.

No matter how diametrically accurate something is set up in the 4 jaw, unless the jaws are perfect there is nothing to say that the work is held parallel to the lathe axis. Truing the jaws individually on the bench is a good way to get the best out of what you have.

Ian P

Mark

The internal ring or the cloverleaf plate idea are both good methods and but work best with chucks in good condition where the jaws are a close fit in their slots. Once a chuck is worn, gripping the ring or plate only loads the jaws at one point so they may tilt resulting in them not gripping correctly along their length.

Using my method the jaws are loaded as they would be in the real world. Using a bright light is possible to true the jaws to pretty fine limits although it can be time consuming!

Ian P

Ian,

It would be wrong to assume that grinding jaws, using any method, will produce a collet chuck. The scroll accuracy amongst other things will ensure it is never really accurate. If the jaws are bell mouthed it will be the chuck body that is worn rather than the jaws - unless the work has been turning in the chuck all the time. This is a subject that comes up all the time on all the forums.

If the objective is to give a new lease of life to an old chuck that is no longer safe to use due to the work wobbling about then it will yield a serviceable chuck for rough turning jobs etc. It will even be good for concentric work if the stock is not removed and the whole thing can be turned with a center at the other end. If this is the aim, then the dremmel strapped to the cross slide is the quick fix with minimum fuss. Hand truing the jaws one by one will take considerable time by comparison and will give no better functionality unless the work is fully inserted over the full jaw length as was the case when the jaws were fitted to the test bar (and at the same diameter).

Mark

Best bet is to buy a Bison 3 jaw chuck from Rotagrip,its worthwhile to also get a set of soft jaws they can be very useful. I understand that Burnerd chucks are now made by east european manufacturers but have retained their own jaw dimensions. I have 6 inch and 8 inch Bison chucks on my colchester master and they have proved to be very good,at one time eastern european chucks were very good value for money but their prices have risen a lot in recent years,but a lathes no good without a decent chuck ,

Unless you are broke I would not grind a lathe chucks jaws ,as if they are that worn the scroll and the slides where the jaws fit are also worn,plus grinding dust on a lathe does not do the lathe much good no matter how careful you are , I have an old 8 inch 3 jaw chuck mounted to a non swivelling base which can be bolted to my mill table ,ideal for holding round work for milling,the jaws were tapered so with feeler gauges I worked out how much the error was ,set up each jaw in a vice on my surface grinder and ground them true,the chuck then gripped work securely ,concentricity does not matter in this case and the grinding dust stayed on the grinder.

Hi Frank,

I'm just rebuilding a student 1800 - the cross slide play (backlash) can be taken up with the two allen bolts in the middle of the cross slide - make sure you can get full travel after each tweak, otherwise if the play is in the slide then adust the gibbs (but you prob know that!)

to sort your chuck you need to use a tool post grinder, the jaws need to be opened onto a ring and be under "open" tension - ive seen modified bench grinders with small grinding wheels mounted onto the cross slide - searching youtube would be a good start, might be worth trying to rig something up rather than buying a new chuck!

hope this helps

Dave

Cross slide adjustment,I looked at my master 2400 today there are three socket screws plus a ball bearing type lubricator in the centre of the slide ,its about 10 years since I had the slide off so memories a bit rusty,I think two outer screws secure the nut and the centre one adjusts the nut, if its different just remove the slide and have a look how the adjustments work,I found that when removing the cross slide the screw sits in a long recess in the casting,and this recess has no drainage and of course it fills with soluble oil and if one of the more higher performance oils has been used it can corrode the feedscrew ,so I made a new screw as Colchesters wanted around £500 for a new screw and nut. And I drilled a drain hole in the casting. And if your Colchester has a hand operated lubricating pump on the front face of the saddle, while you have the cross slide off make sure the oilways / holes in the saddle and crosslide are cleaned out. Also due to space my master resides along a wall and it is a right pain to remove the cross slide and get access to the suds pump and clean out the tank.

Thanks Pete,

I agree completely with your posting with regards to 3 jaw accuracy / runout, Frank in France started the thread with a question with regards to his 3 jaw chuck jaws only gripping at the rear (worn jaws) and some hesitance over purchasing a new chuck! - see posting at top of thread - the toolpost grinder used on the held open jaws should help with his specific issue and possibly get him out of the proverbial.....

Cheers

Dave

OK, I think that's more than enough about what you should expect from our type of standard 3 jaws.

Just like a lathes ways, the chucks scroll and jaw teeth will slowly wear over time and at varying points depending on the size of work you usually use it on. The jaw tips can also wear from work moving around inside the jaws while the chucks rotating. A shaft with a slightly offset center drilled hole with the tail stock center supporting that end can make the work move around for example. No it's not very much, but the work can and will move. The slots and grooves that the jaws slide on also wear. Depending on the hardness, either the jaws or the chuck itself, or even both parts can also wear. But it's very important to note that even the best chucks in the world have clearances built into them right from the manufacturer. Without that very small but important clearance it would be impossible for the jaws to be adjusted.

So, you have to either regrind your chuck jaws or replace the chuck. New jaws can be bought if your chucks a good one and still being made, but that doesn't address the chuck wear. There is only one single method of chuck regrinding I know of that does provide a proper way, and even more important the proper DIRECTION of pre loading those chuck jaws so they can be accurately ground. And it's certainly NOT shown in that YouTube video. In fact it's physically impossible for that method to work and give you correctly ground jaws. Those plates with the clover shaped design cut in it are the only way I've seen yet that allow the internal jaw tips to be ground straight. Due to those built in clearances every chuck has, the jaws tilt a fraction of a degree in each direction depending on which side of the jaws your using. It's not a manufactuering defect they do this, it's just how the design works. So you have to load those jaws and grind to compensate for that jaw tilt to end up with straight jaw tips that grip there full length.

But there's a bit more to this than it first seems. Unless you go the extra mile and do the very best you can while machining that plate you won't get the best accuracy, and that defeats what your trying to do. That plate really should be at least the same thickness as the jaws protrude from the chuck's face,and have properly bored holes with an excellent bore finish so both sides of each chuck jaw bear evenly on it. Just using simple drilled holes could be enough to slightly shift the jaws. Boring those holes is the minimum in my opinion. Regrinding the jaws in a well made chuck is precision work, and it should be treated as such.

So to back this up even more, your very first step is to tear your chuck down to it's basic parts for a thorough cleaning. On good chucks, you should mark each and every part so during assembly all the parts are returned to there exact same position. That's especially important for the pinions. Any chuck that has that mark means that pinion is the master location that the chuck was originally ground to by using it. And using a bit of logic, your going to need to repeat that chuck dis assembly and again clean it after grinding the jaws. So there's much more to doing this correctly than far too many posters understand.

But if you read what I've tried to point out, you should be able to understand that even top quality chucks aren't and can't be all that accurate. But no matter how expensive or cheap your chucks are, it's very important that the jaw tips are square to the lathe ways. If there not then smaller work can and will flex away from the tool tip.

I hope now you know what took me a very long time to research and learn. And none of this are just my opinions, if you care to research it enough, you'll find the same information I did.

Pete

Edited By Pete on 07/06/2014 15:28:37