Member postings for Chris Heapy

I've tried those methods before without success - used a 1/2" diamond lap from the tailstock, and used a die grinder held in the toolpost. The problem I found is that you cannot tension the jaws in their normal gripping configuration AND grind them at the same time. The hollow-ground effect I think is just a by-product of the manufacturing process rather than a required feature. To be honest my feeling is that attempting to re-grind jaws is probably a waste of time because if you have wear in the gripping surfaces I suspect there is also wear in the side slots - which you can't compensate for. Still, it's an interesting exercise.

Chris

Edited By Chris Heapy on 06/06/2013 08:23:55

I found another use for this grinding setup - a poor man's surface grinder

To digress: I bought an old Griptru chuck - something of a mistake because when I tested the chuck the inside jaws were completely useless. The outside jaws (and therefore the rest of the chuck) appear to be fine and hold true, but the inside jaws were so worn they weren't even gripping at the tips and you could see daylight at the ends

OK, accepting the jaws were toast (I will have to look out for a replacement set) I set about trying to figure a way of re-grinding them, and my thoughts turned to the diamond cupwheel mounted on the mill. I checked the squareness of the wheel off against the mill table and as far as I could tell it was nicely orthogonal - although it's difficult to be certain because the face of the diamond wheel is not a smooth machined surface. Nevertheless an 8" square placed against the front edge revealed no errors. Good enough for an experiment then.

I clamped the 3 jaws together and used a parallel to hold them in line, and two clamps to hold the lot down onto the mill table. The 8" square was used again to align them all with the rear edge of the table and overhanging a little.

I could only comfortably take 1/2 thou off each pass - the cup wheels are a bit fragile and I didn't want to break it. Grinding continued until the front of the jaws all looked the same, but by then I realised something wasn't right...

I expected more material to be taken off the bottom edge of the jaws than the top (in the photo above) simply because it was clear that is the way they had worn. However, with grinding complete I expected to see a nice even ground surface but what I got was a definite taper. Oops. It was as if the base (the teeth) of the jaws were not square to the front gripping surfaces. Not what I expected at all. I now realise what I should have done was mount the jaws upside-down onto the parallel because that surface definitely would be square with the inner gripping edge. So I'll have to do it all again.

I've lost nothing though because those jaws really were useless as they stood. I don't know if the jaws are hardened right through or a deep case, if the latter I may well run out of hard steel in the grinding process.

Chris

For plastics you don't want to be using carbide, typically there is far less back rake and cutting pressures are higher thus pushing the work away from the cutting edge. HSS steel would be better, and grind exagerrated reliefs all around (think a knife blade whittling wood!). You cannot take big cuts with a tool like that as it will tend to dig in and pull the tool into the work (and vice-versa), but for shaving/finishing cuts on soft materials it will give you the most accurate result. Needless to say the cutting edge has to be razor sharp, and it will be fragile. If you recognise its limitations such a tool still can be useful. I use such a tool for cutting PTFE (carbon/bronze-filled PTFE) when forming seals and piston rings.

I suppose I should check mine against a DTI to see what sort of accuracy I can expect from using it. That last thou or so movement is tricky and I have yet to see zero movement on the dial so I don't know if that is me, the bore, the probe, or mechanical linkages within the instrument.

I cleaned and lubed mine (as suggested above) and it does seem to be less sticky in operation.

Ooo - new kit arrived

and this is the type of thing it will be asked to hold for machining. Just waiting for a backplate to arrive now.

It might be an old design but it is the newer bi-metal blades which make them work well. The old carbon steel blades never did take kindly to being continually bent around the wheels and guides and would snap regularly - especially if over-tightened to the least degree.

The saws (the blade guides) do need careful setting up to cut accurately though, I use a parallel length of barstock I slit up the center for an inch on the mill, then drilled a hole for a clamp screw. This is then clamped onto the blade and a square placed on the vice bed will then indicate whether it is set orthogonal to the vice. You have to do this near each blade guide, and the guide assemblies themselves are crude affairs requiring judicious taps with a hammer (after loosening the bolts) to get them lined up. However, once done the saw will do its stuff and cut very accurately.

Buy/make yourself a mandrel handle for the lathe so you can turn the spindle by hand easily, you'l find it one of the most useful accessories for threading operations.

Another way - possibly better than using the vice - would be to mount that piece of steel lengthways along the bed, standing on a packing piece and use a clamp at each end, then use the endmill flutes to cut both sides of the workpiece without having to re-mount it. The result will be as accurately parallel as your machine is capable of milling.

For the 'flip', just mill the piece as usual held in the vice, then rotate it 180deg (like a propellor blade in front of you ). Any inaccuracy would be equalised and the result (should) be a parallel bar.

Yes, use a stout boring tool. Be wary of parting off dead to the length required, a facing cut will probably be needed if surface finish is important. I have a 1" 2MT shank endmill which I plunge-cut start a recess like that, then I can use a larger diameter boring tool. However, 3" dia is too big for me to part off comfortably, I would tend to saw the blanks off first and work from there.

Looking at that machined workpiece... your chips are like dust which means the endmill isn't cutting like it should. Looks like you cut it dry... and the stringy swarf again suggests the cutter isn't cutting cleanly. The finish doesn't look good either (difficult to tell from one photo at one angle), it should be smooth and shiney. Might be too high a speed on the cutter, might be a blunt cutter, might be very 'sticky/gummy' steel. Best to play around with different parameters on a piece of scrap )of this material) to familiarise yourself with what works best for it - they all respond differently.

For your machined parallel - if you turn the piece end over end (180deg flip) it will come out parallel even if the bottom of the vice is not perfectly aligned with the lathe bed.

I've never had an issue with the blade guide bearings other than adjustment, but have to admit ball bearings are not the best solution. The larger models use carbide blade guides which are more accurate.

These 6x4 saws are incredibly tough wearing, I've cut 6" stainless bar - not once but many, many times (but I had to turn the piece around to cut all the way through of course). One blade would last maybe 6 cuts before it was too blunt to use (or it snapped) and the motor tended to get a tad warm-ish These 2" slices were sawn from 6" bar to make telescope counterweights and after sawing them off my poor little Myford was then pressed into service boring them out and turning all over to a nice finish. The saw cuts were accurate enough that maybe 20thou had to come off to true them up - depends how accurately I managed to line the cuts up after turning the bar. I know I should have used a bigger/beefier saw but I didn't have room for one, but it shows that if it doesn't fall apart shortly after buying it then one of these saws will likely last many years.

Edited By Chris Heapy on 03/06/2013 17:08:13

Edited By Chris Heapy on 03/06/2013 17:08:42

I like flycutters for the pretty surface finish they leave but unless your mill head is set exactly square to the table the surface will not be as flat as a surface machined using multiple passes with a narrow(er) endmill. Also, I hate the way flycutters throw chips all over the wrokshop! Generally I use a re-ground cranked lathe tool, either HSS or carbide tipped (I know carbide is not ideal for interrupted cuts but they seem to survive quite well in my experience, and it only takes seconds to sharpen them if they do chip). I used one for the backplate for my tool grinding setup (adapter for the mill) and that was 4" x 18" long - a relatively big surface area for my small A2S mill. Took it in one cut each side.

Edited By Chris Heapy on 03/06/2013 12:41:35

I use straight cutting oil but only when I have to - stainless steel mainly. On my saw adding cutting oil can make the blade slip off its wheels which means the messy job of opening it up and re-fitting it. The blade very rarely (if ever) slips off otherwise.

I've got through quite a few blades on my saw over the years, at least a dozen coarse 10tpi blades which I used for cutting aluminium, I didn't have a lot of luck with 10tpi and can't recommend them because, although they cut faster, they seem prone to breaking far more often. However my current standard blade has been on for at least a couple of years, sometimes you get one that seems to last forever.

I keep a fine sharp blade especially for cutting brass - well, large section brass anyway (I can't be bothered changing it for the odd bit of rod). A blade that has been used on steel struggles to cut if it is later used on brass.

Tracy tools do loose sets, have a look here: **LINK**

Sounds like you don't have enough clearance behind the cutting edge and it is just rubbing..

Depnds on the job - how long, how deep, how thick the blade is and whether it's a new (sharp) blade.

Thin blades (50 thou or less) can be a problem because the cut can wander off line - of course the arbour won't let it so the blade twists and distorts. The deeper and longer the cut then the worse this problem shows up, and compounded if the blade is even slightly worn because it can end up cutting better on one side than the other thus increasing the likelyhood it will wander.

I found the best way is to take a shallow cut first (about twice the depth of the teeth) and the second the full depth. For the first shallow cut the blade is not under much stress so will (hopefully) cut straight, and for the second the shallow cut already made will help guide the blade for the deeper cut. Have only as much blade exposed as required to do the job - this might mean machining larger supporting collars which will help keep the blade stiff and aligned. Yes, use plenty of lube and take it slow.

With thicker blades (3/32" and up) the wandering cut problem starts to disappear, and if you buy blades with side-clearance teeth you'll get improved chip clearance and cooler running.

Looks like Norman wins the prize I think that would do just fine - provided it doesn't add to the overhang too much.

Chris

I suppose I should add that I tend to use the 4-jaw a lot for this type of work, and whilst a definite improvement over a 3-jaw SC chuck (an extra jaw for support, better accuracy) it is slow to set up and there is less 'feel' about whether you have over-tightened the chuck, additonally much more work if you need to remove the workpiece and re-mount it a few times. Cutting threads on tubes/rings for optics is the main job here - lots of different diameters, some fairly thin tubes, precise threads required that don't take well to being squished in chuck jaws. I'm not looking for perfection - just an improvement and ease of use.

I specifically want the 6-jaw for holding alloy tube which tends to distort in a 3-jaw, but it will come in handy for other work too - particularly delicate rings and discs. Yes, there are alternatives and I've been using them for years - which is why I recognise their limitations and want the chuck.

It isn't too heavy for the S7, especially with fairly lightweight workpieces. I would be reluctant to run it at top speed perhaps but all in all the 5" 3-jaw I posess has performed faultlessly and is the same weight. I would rather not have the added overhang caused by fitting a backplate but it's unavoidable.

The register on my existing chuck I machined the backplate a close fit in its recess so it cannot readily be adjusted by the 'loosen the bolts and tap with soft mallet' method. That is why I was thinking of not having it such a close fit on this one and indeed having that technique available to me. I think we have to assume a decent chuck is machined axially true - there isn't much we can do about it (well, not easily anyway).

Martin, the register is only nominally concentric with the gripping circle it may not be optimal in a 'less than premium' chuck. The quoted accuracy is 0.025mm TIR and there is no Griptru-type of adjustment. If it were a Burnerd I would be more inclined to trust it (but note that even with such a premium chuck there is apparently a benefit in having it adjustable - Griptru/Set-tru etc.) There may be something to be gained by tweaking the mounting - but quite possibly not if the run-out is not stable at all diameters as can be expected on a cheaper chuck.

Bazyle - you've stirred the memory now! I seem to recall a method for a DIY Griptru ajustment published years ago. I'll have to search the archives.

I'm buying a new lathe chuck for my S7B, and the one I want is not available in Myford fitting so I'll have to machine a backplate for it. I've done this once before years ago but am considering the job again new. It looks like a suitable 5" backplate is available pre-machined to fit the spindle (Chronos list one), and while last time I machined everything from a raw casting this might be a time-saver if the quality is good.

The chuck is a TOS 5" 6-jaw, selected mainly because I do a fair bit of work on alloy tubes and a 6-jaw is better suited to gripping thin tubing. I would love a Griptru Burnerd 6-jaw chuck but the price new is silly (over £800 new), and I already have a 5" TOS 3-jaw for the S7B and I've never had an issue with the build quality of it.

I was thinking for alignment, after machining the backplate register to fit the recess, I could put a 2MT test bar in the headstock and grip that with the chuck jaws while the holes are spotted through (it's a front mounting chuck), remove the backplate for drilling and tapping, then re-mount and use the test bar again to hold the chuck whilst the bolts are tightened.

I know I should be relying totally on the rear machined register of the chuck to provide the alignment datum point but then thought it might be an idea to use an actual workpiece clamped in the jaws as being a more representative/useful datum? In fact, if the backplate were machined a couple of thou undersize there would be room for subequent adustment should the chuck start to run out after a period of use. I figure the chances of it shifting in use are minmal with 3x8mm bolts fully tightened.

If anyone has their own ideas as to how to go about this job for best results I would be interested to hear them.

Chris

Edited By Chris Heapy on 01/06/2013 10:23:45