Workholding questions!

Got my four jaw chuck out of the box for the first time on Sunday with the aim of cutting a short, round bar into a rectangle (to create a tapping block)

First problem was that the four cap screws supplied with the chuck don't fit the lathe (it was bought with the lathe and they are too long to fit behind the spindle plate grrrr....)

While I am waiting for the new ones to arrive (there were only three on the 3 jaw chuck) I started thinking about mounting my job - the bar is perhaps 30mm in diameter and 60mm in length and I have managed to mount this in the 3 jaw and (gingerly) faced either end, and then started to mount this in the four jaw.

Because of the length I reversed two of the jaws to get the clearance, but the other two do not grip anything - I can close them to touch the bar to stop it moving beween them but am a bit concerned that if I wind the speed up it will not hold being held just at the ends, any suggestions? Or is this the normal way of doing this? I guess once I have one or two 'flats' I will be able to mount it much more securely.

The other question (which has been asked before and caused some debate) is whether I will be able to do this sort of interrupted cut using indexable carbide tools (as this is all I have at the moment)

Any suggestions gratefully received!

Thanks

Chris

Whats the lathe? is the chuck held by screws passing right through the chuck into the spindle flange or nuts behind the flange onto studs in the chuck backplate.

You should not use it with the work only held by two jaws, I assume the unreversed jaws come below the centre of the bar so don't grip. Suggest you clamp the bar to the cross slide and flycut the face.

It is also possible to hold the bar across the face of a 3-jaw but not really best practice particularly if you have a small chuck/

Should not be a problem with interrupted cuts.

J

Edited By JasonB on 18/02/2013 09:32:52

I do on occasions machine metal flat, or face the side of a bit of flat, and often the three jaw will do the job OK. For interrupted cuts carbide works, but I usually use HSS unless the steel I'm using is a bit too tough.

What size chuck do you have? Once you have a flat on one side, there will be no problem with the second side. Can you open the reversed jaws far enough to get to the second step, even if the jaws are only held by a thread or so. Ian S C

That's the conclusion I came to! Yes, the side jaws are well behind the centre of the bar.

The lathe is a Sieg SC4

Interesting idea about the crosslide and flycutter, I don't have one and anything to mount work on the crossslide but think this is worth pursuing...

Could I mount a fly cutter in the 3 jaw chuck or would I need a drawbar through the spindle or a collet chuck? What is a good way to mount on the crosslide? If I get a angled block with a V (is this a 'Keats' block?) will the clamps not get in the way of the flycutter? Any suggestions as to type/source of flycutter? I did wonder about drilling some holes to bolt it down but would like to avoid this if I can get away with it.

Being a beginner sometimes it seems every task I tackle requires something I don't yet have but I guess this is the way when you are starting up!

Ultimately I guess it would be the sort of job you would do on a mill but I don't have one of these yet either (this will be considered sooner rather than later, as it seems necessary to do a lot of things)

Thanks for the help

Chris

Sorry to follow up my own reply!

The chuck is held on to the spindle plate by bolts going through clearance holes in the spindle plate into tapped holes in the back of the chuck, the three jaw had 3 M8 * 16mm hex bolts that (just) fitted between the spindle plate and the headstock, the four jaw came with four M8 cap head bolts that are too long to fit - I can cut them off/grind them down but don't have a grinder yet either!

Not a big deal, I have some shorter bolts on the way but I was slighly irritated that I bought the chuck with the lathe and as it was supplied it can't be fitted!

Chris

Ian - the work is currently already on the second step in the jaws?

Do you mean to try and get it in far enough so the other pair of jaws are across the center line of the work?

Not sure this is possible but I'll have a look tonight and perhaps take a photo?

Chris

Put some packing between the work and the two jaws that don't touch

Would suggest you fit studs into the chucks and faceplate. Make spacers if needed to fit in the back of spindle holes, the just use nuts. Much quicker and easier than fiddling with the cap head screws.

John they will touch but don't come below the centre line of the bar so will tend to push it out and packing will tend to rotate and do the same.

Cheap flycutter in teh 3-jaw has worked for me a number of times. I'll look up the cross slide slots on teh SC4 and come back to you re holding.

J

Hi Chris,
You could make two packing pieces about 6 mm thick and 20 mm wide with a length that went from the face of the chuck to a little way in front of the centre line of the bar. These would effectively extend the two non reversed jaws. Also make a packing piece just under 30 mm wide (Say 29.8 mm) to separate the ends of the first to packing pieces at the end in contact with the face of the chuck.

Les.

Clamping will depend a lot on what you have available. Pack to bring the work upto the lateh ctr height

This is not ideal as there is a risk of the bar moving, use two clamps not just the one as shown.

A Vee block would be better but use a small flycutter to avoid hitting it, again use two clamps

Stood on end is another possibility, two clamps again

Or hold in 3 jaw

Wow - what a helpful lot you are, this has given me loads of ideas - I would not have thought about the three jaw like this, and the clamping kit images are very helpful

I do not have any parallels (is that the correct term for the block with the holes through?) or a clamping kit but as I intend to buy a mill this could be a possibility. Think the SC4 has 6mm T nuts but am not sure if this is the diameter of the bolt/gap in the slot, I'll stick a vernier on it when I get home. This is what is listed on the US Travers site

Think the quick and cheap approach is in the 3 jaw but how secure is this? do you think I could do all four sides like this?

Second option would be buy a clamping kit, V block (and perhaps parallel/block with holes) but I wanted one of these anyway to use in the machine vice I have on my bench drill as packing.

As you say, the main problem is stopping the bar moving but a V block would prevent this?

Might try the 3 jaw approach while I think about the second approach, as I can see all these tools would be useful in the future anyway?

Chris

Chris, DO NOT mount fly cutters and milling cutters in a 3 jaw chuck. Disaster and real danger, not namby pamby elf 'n sfety, that way lies. If you have to use your lathe in this way for goodness sake get a collet chuck. The mere fact that somebody does mount tools this way and gets away with it is simply thier good fortune.

Thats known as a 1-2-3 block, parallels tend to be longet and thinner typically 3mm x 150 x various heights but anything to hand will do.

I think I have only used that 3 jaw method with flat stock whick means mor emetal in contact with teh jaws, it can also be done with your 4-jaw and should allow all jaws to contact and would be a better bet than the 3 jaw.

If you do o with the 3-jaw just take light cuts and only take enough off until you can get it in the 4-jaw.

OI would think your 6mm tee slot applies to the thread M6 with the slot being 8-10mm to take the neck of the tee nut.

Mike I understand the milling cutters as they are hard and will not run concentric but why not the flycutter

Its possible to make a flycutter using a bit of a broken HSS tool, anything will do, a tap, drill(flute end), center drill, end mill, and a bit of ingenuity, does'nt need to be fancy, you may only use it once, then put it in a draw just incase, you'll only need it again the day after you chuck it out. I'd go for doing one side in the three jaw, you can then if you like (a bit more secure), use the four jaw. If you go the flycutter way, you might be albe to attach it to the tool post, I have on my lathe, but its much bigger. Ian S C

Jason, there a real, and I mean REAL, risk of the cutter coming loose in a 3 jaw chuck. Before anybody tries to draw an analogy with a 3 jaw chuck in a drill, remember the cutting action of a milling cutter is not the same. The impacting on single point cuting edges and the side thrust can loosen the jaws without warning. Lathes for turning only, unless you use a collet chuck. HTH.

So what about when I want to turn something eccentric or intermittant in the 3 jaw. That will give similar loads and interuptred cut.

J

I do think you are making a rod for our own back in many ways. You don't need a clamping kit on day one - just any old bolts nuts and washers. Those fancy clamping dits were only invented recently. You don't need parallels, just lumps of square BMS which will later be available for projects if you do get better kit.
As Ian says you can make a flycutter in two shakes.
You don't need a tool grinder to start sharpening. An angle grinder wheel or a small stone in a drill, even a sanding disk can gently sharpen a broken drill into a clycutter tool.

In fact going back to the start with your too long screws either shorter ones from DIY store/bike shop/garage would do and anyway you can saw the long ones off with a junior hacksaw and clean up the end of the thread with a triangular file.

Anyone worried about elf and safety as mentioned above please immediately switch off, unplug cut the plug off your lathe as it might dangerously start rotating if you don't..

Thanks, your message made me smile and I understand what you are saying.

Bearing in mind I am starting to collect nuts, bolts and washers, and actually do not have any square BMS (but a fair amount of round bar which I scrounged) which was the original question really, how to turn the round stuff square!

I really have only just started - even to the point of collecting nuts and bolts and of course can use a hacksaw and file and clean the end with my Dremel - which I have been using to sharpen my parting off blade with reasonable success. That comment was more in reference to a Sunday spent tweaking things and looking for bolts etc rather than actually making something interesting, I am sure you can all relate to this...

I have seen several plans for a flycutter which I think I could tackle. but thought it was worth asking about alternative work holding techniques (although I seem to have sparked a debate about using fly cutters in the chuck!)

I have lost count of the number of holes I have put in my finger when drillng PCB's with my Dremel, if there was no blood and pain it would be no challenge and no fun <g>

I will stick my bar in the four jaw and try this first, if It doesn't work I will try something else!

Regards

Chris