Poor finish using indexable lathe tools on steel

+1 for the sharp polished inserts sold for aluminium. As said they work a treat on steel. Was doing some 50mm diameter mild steel this morning and the finish was superb, but you need to be careful since the edges can be damaged quite easily if mistreated. And yes keep the speed up.

Doug

Again, many thanks for the loads of helpful and informative comments, had not expected such a quick and extensive response. Making an action list for the next bit of turning to be done. Will check the insert tips again too. they are 0.2mm radius.

Will be a few days before I can get in the workshop again though.

XD 351 was right, tip chipped off by the time I took the facing cuts.

One of the problems of using TCT is that stalling the spindle always results in a chipped insert. That is especially troublesome on hobby sized lathes. I am using carbide less and a tangential HSS tool more.

If the chips curl back and contact the work it can mess up an otherwise good finish.

By the looks of what you are doing, that steady support is not needed. Avoid where ever possible, cutting to the very centre unless it is needed. If it is not required to be flat to the centre, I use a centre drill and put a 2mm or 3mm diameter dimple in the end of the part. RPM wise, anything from 300 rpm to 600 rpm is plenty fast enough. You need a roughing out insert and a finishing insert. Roughing is often a 0.4mm radius. Using a water soluble type coolant will help reduce the heat of the work piece. Hand feed at a rate that will make little chips, not long curls. It maybe that you will need the smaller R0.2mm insert to get nice curled chips. Some where around 0.5 to 1mm on diameter will do that, but the depth of cut is limited to the power of your motor. For 1mm diameter of cut, you will need around 1 hp,/750 watt motor. If you have the 3/4 hp motor taking a 1mm cut I think is being unrealistic.

Use a new sharp edge for the finishing, and take the finish cuts at 1/2 to 1 radius per side and a feed rate of 1/4 of the radius as a feedrate. So if you use a R0.2mm insert, then taking a 0.2mm on diameter cut for the finish pass at around 0.5mm/rev at around 400 to 500 rpm will work well. Using a cutting oil for steel will aid in the surface finish, or a water based cutting oil at around 10% concentration will also give a good finish. 500 rpm at 0.05mm per rev will take about 1 min to travel 25mm.

I don"t run my Super 7 any faster than the highest speed on the spindle with the low speed of the motor to the clutch. I don"t run the faster speed from the Motor to the clutch on anything these days. Some materials will give a better finish with dull looking edge insert tools, but I mainly use the very sharp carbide for Aluminium on most steel's on my lathe. The coolant I use is one suitable for Titanium and steels and Non Ferrous metals works really well.

Neil

Pete,

You still need to address the stalling / belt slip issue.

You have to be careful with carbide feeds and speeds, the charts all assume sufficient power is available, as in industrial power not hobby. You might loose a few tips before you workout exactly how much depth of cut you can take on your machine.

Achieving much better finish now on 3" diameter EN1A bar, speed upped to 1000 rpm, depth of cut 0.020, feed 0.004 per revolution. Facing cuts at same speed and depth of cut, by hand feed (no power cross feed).

So thanks again for assistance. Stanley steamer front wheel bearing cup driver nearly finished, car will be on the road again very soon!

This all started when I took the front wheels off her to regrease them the other week, found a bearing had been damaged by water getting into it, and had to start making a bearing cup driver and a new dust seal plate.

Edited By Peter Turvey on 23/04/2019 18:57:39