Newbie- 7x12 tools needed

[txcwboy]

I have the 7x12 from online site ,used to be cummings. I forgot the name. Its blue. Anyways ...I need a cut off bar and holder. I have no idea what to buy. I ve had it for several months and still havent really used it. I need cutting tools also. Its 110 degrees in my garage so I havent felt like being out there. I dont need high dollar just decent product. Help me please !

THANKS

Dave

[wildwestpat]

Hi Dave

I suggest you look to mount a conventional cutoff parting tool upside down and run the lathe in reverse. I know this sounds odd but helps a lot with avoiding the risk of a dig in as the parting tool moves away from the work when run upside down with the lathe running in reverse. Bigger lathes are able to use a tool post on the far side of the work to achieve the same effect and it is almost allways used for parting off as the tool moves away from the work if there is an iminent dig in situation. You need to get the cutting edge set at centre height and this will dictate the size of the holder. Measure centre height with respect to tool holder clamp face i.e. bottom and chose a tolder that will let you mount it upside down.

Good luck and hope your workshop cools down a bit soon it is cold and wet this side of the pond this summer!

Regards

Pat

[TroyO]

I use a similar method for cutoff and for threading.... I call it Australian Threading... upside down and backwards. (Comes from Down Under...)

It works pretty well on my 8x12.

[xl97]

can anyone expand on this..

I currently have a AxA QCTP on my 8x12/14

and parting has been an ugly scene for me..

either the cut-off blade is digging into the part...or I feel the QCTP pulling..or its making terrible noise and doesnt seem to be 'cutting' well..maybe more tearing..

I center my cut-off blade tip to center line..
lock my carriage
and slowly feed..

still no joy.

anyone got some images to help me visualize what you guys are doing?
Thanks

[txcwboy]

I did buy a parting tool and holder and an indexable set of cutting tools.

Thanks for help

[TroyO]

Heya XL...

Are you also making sure the blade is 90 degrees to the work as well?

The easiest way to do that (For me at least) is to line it up against a faced off part. I usually loosen the QCTP bolt then crank it so the side of the toolholder is flush to a faced off surface then tighten it back down.

In other words it must be exactly | and not \ or / at all.

Also... sometimes it helps to have the cutoff blade slightly higher or lower than the centerline to compensate for flex.

If you have the usual cutoff bar made of solid HSS you can make a slight cup just behind the tip where it cuts.

Use WD-40 (or other lube)

For the reverse cutting... the cutoff tool is mounted upside down in the toolholder. The lathe is run in reverse. That means any pressure will be pulling up and away from the toolholder etc..... so it doesn't dig in much.


Also... the chatter can sometimes be fixed by INCREASING the feed... as counter-intuitive as it sounds.

[wildwestpat]

Hi Dave

Parting off is a surefire test of both skill and machine so don't give up and revert to the old hacksaw.

TroyO is dead on in that the parting tool needs to be square with the lathe axis. It also needs to be perpendicular (vertical). In the vertical plane it needs to have some clearance on both sides. The HSS cutter should have a small taper and the mount should ensure that the taper is divided equally between the headstock end and the tailstock sides of the intended parting off grove. Sorry if this is labouring the point but I have seen tool holders that are not very good in this respect and have required the base machining to suit the available HSS tool piece.

The upsidedown parting off with the lathe in reverse does work and avoids much of the chatter dig in problems.

However you might care to tighten the gibs on both the cross slide and the compound. There is a tendancy to set these gibs too give too light a pressure in the interest of being able to spin the handle easily. Also ensure that the compound is centered above the dovetail block of the cross slide - maximise ridgidity.

Have you checked that the headstock bearings have a sufficient pre-load as these can be a source of chatter in a new lathe. Chatter is most likely to show up on parting off rather than normal cylinder turning.

TroyO's advice to keep a moderate feed rate is also good. I would add that once the parting off cut has been started do not hesitate but keep advancing the tool so as to keep cutting as a continuous action. Cultivate turning the cross slide advance with both hands so that the motion is very very smooth. The use of two hands will also help prevent any temptation to have the other on the saddle hand wheel.

I suggest you try a few simple checks to ensure that there is no detectable free play in the saddle - cross slide - compound slide - when tugging at the tool rest. Often a new lathe will require some adjustment but the newer lathes eminating from the far east do not in general require the dovetails to be polished as in earlier threads on this and other web sites ciurca 2003/4 era.

Good luck

Pat

[xl97]

Hey Troy-
(figured you were dead..since Ive tried contacting you like a million times!) LOL

anyways.. I'll give the upside down parting off a shot..

[TroyO]

LOL... nope, not dead. Did you not get the reply to the last PM you sent me on here? Bummer.. LOL, It was long winded too.

I'll shoot you another PM, just maybe not so long.. LOL.

Anyway.. overall done with the stuff that had me out of town/unavailable and back to getting to work on various projects. Soon to include the ReplicantFX project .

[xl97]

man..if you get back on the RFX side of things.. I could 'really' use some help..

code that worked previously..before taking a break.. is now NOT working.. when I declare a variable..the sound breaks in PLAY2.. and I need someone to confirm.. but there IS NOONE!

lol

edit: nope no PM's..anywhere here, RFX, or email.. but should be in you sent items box...

[wildwestpat]

Hi Dave here is a picture to help. You will see that I have a needle thrust race instead of the supplied stock washer to increase the clamping force from the tool post thread. To adjust the height of the upsidedown cutting edge I find that an 0.125 inch plate with a suitable hole in it is enough to raise the whole tool post and bring it in on center for this tool. I did not show it in the photo as it is made of gauge plate and I keep it in a bit of greased paper. Did not want grease all over my camera!

Hope this explains further.

Regards

Pat