Member postings for old mart

When cutting metric threads, I would always use the same number on the thread dial.

The Smart & Brown model A that I use does imperial and metric threads, I have a 120/127 compound gear for it. I cannot understand why there is any difference between imperial and metric threading, and anyone who cannot read a thread dial shouldn't be using a lathe in the first place.

The S & B also has a single element half nut with a bronze slipper on the other side of the leadscrew. I am always careful engaging the leadscrew nut fully as it can drive the saddle even if not aligned., This happens frequently when using the leadscrew for ordinary turning and doesn't matter in that application. If fully engaged, it has never slipped out of drive, even before making the new nut.

I disengage the leadscrew nut at the end of each pass, withdraw the threading tool and run the saddle back by hand, leaving the spindle running and not reversing. This is easier for me than reversing and withdrawing the tool simultaneously.

The higher speed would be an advantage especially if using small solid carbide cutters. Reducing the feed rate would make up for the lack of speed if need be.

I am facing the opposite problem, The Tom Senior light vertical which I am working on has only 4 speeds, the slowest of which is over 500rpm. A bit fast for larger drills and cutters in steel.

If modifications to the spindle are required, then the use of another lathe big enough to do the job is required.

As Ketan advises, the original type of bearings would be good candidates, especially as the original bearings had a long life.

Proper carbide inserts have sophisticated tip geometry which hss and brazed carbide cannot match. Only first generation inserts such as TPUN lack the advantages of modern types.

The Smart & Brown model A that I use has a new leadscrew nut and no endfloat in the leadscrew, but I wouldn't dream of leaving it in gear when reversing. Why? Because there is backlash between the spindle and the leadscrew through the gears.

Its easy to check, just set up for threading, turn the chuck by hand until the saddle moves and then turn the chuck the other way. See how far the chuck can be turned before the saddle starts to move. Using a dti will give the most accurate results. The finer the thread pitch set, the greater the backlash errors will be.

Edited By old mart on 17/06/2019 12:51:36

I had to replace the bottom taper roller bearing for an R8 mill spindle, the wait was a week for SKF, so I chanced it and bought Chinese, and it has been running fine for 5 years.

If an ebay listing similar to Hollowpoints' is available in OZ, it would be a good choice.

I always try to buy 20mm holders and then mill them down to 18.53mm which is the exact height of the Smart & Brown model A which I use.

I have milled down at least 25 down, including Kennametal, Stellram, Sandvik, Iscar, Korloy, Seco, and others including Chinese, and they are all similar hardness. I use a Ceratizit 50mm shell mill with 5 RPHT12 inserts in it. The inserts can be indexed six times per set, and milling down just one tool uses up an index.

If you only have hss, then keep a good flow of coolant and use a very slow speed.

I bought a set like that years ago, they were rubbish, I threw away some and gave away the rest.

This type of set costs more but at least has the codes on the sides so you can buy more inserts.   

There are a lot of tools with inserts which look alright to the novice, but make the more experienced of us want to puke.

Ebay UK 263527683427 (I tried twice to cut and paste the listing without success)

Edited By old mart on 16/06/2019 11:45:56

Edited By old mart on 16/06/2019 11:46:23

Edited By old mart on 16/06/2019 11:50:30

Try out the settings first by just touching your threading tool on a bit of barstock to leave a mark that will enable the pitch to be checked. 1.5mm pitch will be 20 threads per 30mm length.

Anyone still frightened of buying Chinese tools and inserts could try APT, they are very good. They also sell smaller quantities of certain popular inserts specifically for the home market.

Something with a backgear would be preferable for threading. The backgear on the lathe I use slows the spindle by a factor of 7.1, down to a minimum of 30rpm.

It's nice to know that a British importer stands behind their products, well done Warco.

 By the way, if you make a note of the number on the belt, you can get a replacement easily.

Edited By old mart on 14/06/2019 21:15:57

Have you tried Chester tools?

1" marine ply will be plenty strong enough for the weight unless the bulkheads are 6 feet apart.

Could you drill two sets of holes in the shelf, front and back and use bolts and wingnuts to secure the lathe in either position?

The quality of cheap Chinese inserts has risen sharply in the last couple of years and the prices are rock bottom.

They are great for hobby use, and the aluminium specific inserts are fine for use on steel and can easily manage a finishing cut of 0.0005".

I'm a user of motorcycle chain lube, the old PJ1 blue label went on like penetrating oil and hardened to a waxy coating. Sadly, they have changed the formula. What is the make of the Teflon type you guys use?

It has the added advantage over oil in that it quietens gear noise better.

Shafts which are lubricated with oil should not be greased, I am only recommending grease on exposed gears.

Edited By old mart on 13/06/2019 22:47:44

At first glance, the bushes inside the quill pulley seem to be excellent, no discernible play even on the thrust axis. More checking will be done when I strip down the head.

To maintain the 18+" of X movement with nearly 4" of combined nut length, I will have to increase the length of the leadscrew thread by 4". The two nuts will end up with a gap of about 1 1/2" between them to allow access to the Y axis nut fixing screw and washer. One nut will be fixed and the other will be screwed into a sleeve using a fine thread, maybe 28tpi and have something to lock it. I don't think there will be any way of adjusting the antibacklash without removing the bed. This should not be a problem as the combined length of nut thread is somewhat overengineered.