Milling for beginners

I'm also lead to believe that when tapping mode is selected a separate torque setting on the chip comes into play which should give it a bit more wellie to turn a larger tap at slower speed.

JasonB: Thanks for the explanation, think I understand now. I'll have to wait and read the article in MEW when it arrives.

Oxymoron: Tapping heads come in a huge range of styles and functions for lathes and mills or drills. Here are mine for use on milling machines:

The one on the right is for CNC mills and is a tension/compression head. It is rigid in rotation but has some spring loaded compliance axially. So if your CNC mill doesn't do rigid tapping (mine doesn't) it allows you to tap and then reverse while compensating for slight differences in feed rate versus thread pitch, and for the slow down, spindle reversal and speed up without having to match the feedrate all the way. The other two are for use on a manual mill. They incorporate forward and reverse clutches and a variable torque limit. In use the tap is held in a rubber/metal collet. The depth of thread is set on mill quill stop allowing for a couple of millimetres overrun. Then with the mill running the tap is fed as per using a drill, although you need to roughly match the movement of the quill to the self feeding action of the tap. Once the stop is hit the tap drives another turn or so and then the forward clutch automatically disengages. A sharp upwards movement of the quill engages the reverse clutch and the tap is reversed out. The reversal of direction is internal (no need to reverse the mill spindle) and is usually at a faster speed than forward. For the unit on the left tapping is at the same speed at the spindle, the reverse out is at 1.75 times the spindle speed. Each tapping cycle only takes a second or two and no reactions times are needed.

There are also tapping units available for lathes, although I don't have any for the manual lathe. For the repetition lathe the tapping head is much simpler, basically just dog clutches, as shown here with the cover off:

This is a non-reversing unit, but the main spindle on the repetition lathe is reversed by flicking a switch on the headstock. It's more or less instantaneous as all it does is swap two phases on the motor, brutal but no need to stop the motor before reversing as it's designed for such operation.

I expect someone will now step in and 'complain' that this isn't milling for beginners.

Andrew

Makes you wonder why that isn't provided for all operations as a matter of course, unless it's a thermal capacity issue with the motor.

Andrew

Andrew thanks for taking the trouble to post the pictures and explanation about Tapping heads. Very interesting for me.

Jason, have you come across a decent manual for the SX2.7 anywhere on the net? The manual that comes with it is very sparse apart from the exploded component diagrams. I managed to download a better manual for my SC4 lathe but not found anything for the mill.

Dave

Andrew, that was my thinking. When tapping the chip possibly allows a higher current draw before the safety trip kicks in and if used for too long a period things could get a bit hot.

Oxy, I have not actually had a look for another manual but will have a search of a couple of likely suspects to see what I can turn up

Well I had a little play with the tapping function today and was pleasantly surprised, the mill had the power to drive some quite large taps and the whole thing was quite relaxed at reasonable speeds. I know Ketan likes to do everything at 5000rpm since he got his grubbies on the SX3.5DZP but I started off with the following.

3 holes drilled 4.2mm and tapped M5 x 0.8 @ 100rpm, spiral flute tap

1 hole drilled 15/32" and tapped 1/4" BSP @ 100rpm, spiral flute tap ( one hole I did not mean to drill)

2 Hole drilled 10.3mm and tapped M12 x 1.75 @ 100rpm, hand taper tap

1 hole Drilled 2.5 and tapped M3 x 0.5 @ 120rpm, spiral flute tap

Material probably 6062 aluminium 6mm thick and a splash of Rock-oil Maxcut No5 tapping fluid.

As per my earlier post the only tap that seemed to bog down a bit was the M12 taper tap though the machine did seem to pulse the power and it showed no sign of stalling.

Edited By JasonB on 23/12/2018 11:36:50

Jason, many thanks for investigating 'Tapping Mode' and posting the video. Those Spiral flute taps look impressive, will be checking those out for the next Tap I need.

Regards Dave

+1 on spiral flute taps, been using them for 15+ years. Very good for machine tapping at roughly the same spindle speeds as for drilling. They are also fine for use by hand, especially in blind holes as only one tap is needed to get within a pitch or two of the bottom. Since there is almost no lead in they do require a bit more care when hand tapping to ensure that they are perpendicular.

They make good hobs too:

Andrew

That is a really nice feature on that mill, very impressed with that.

Ron

Seeing Jasons video of the tapping feature on the SX2.7 mill I am tempted to fit a reversing switch to my SX2P which I understand is a very easy and simple mod. It would certainly be good to have that facility on the mill, though I dont know if I would be brave enough to use it in tapping blind holes.

Will just adding a reversing switch work on the SX2P? Inserting and withdrawing the tap will have to be performed manually. Unless the head is perfectly balanced, with little or no force required to lift and raise it, the tap will not self extract when the motor is reversed and will most likely spoil the thread. Trying to manually extract it under power whilst matching the rate of insertion will i think prove equally difficult.

That did cross my mind as the SX2.7 is only pulling and pushing the quill up and down and not the head. It may not work on mine but it will be worth a try, since I changed over from a lever spring to a gas strut the head is well balanced, maybe not perfectly but it is quite light now.

I’ve been surprised at how much better spiral taps are than standard ones. I only have a few metric ones, I’m not sure if they’re available out here in Whitworth, but guess if they are they’ll be prohibitively expensive.

I've never broken a spiral tap, wish I could say the same about standard ones.

Don't know where "out here" is but in the UK Whit would be about 10% more than a similar diameter metric one which is not a lot.

I came across some fluteless taps today which surprised me, first time I have seen those.

Jason, can you tell me with SX2.7 in tapping mode I guess reversing the tap is done by pressing one of the green buttons in the end of the handles..? I ask as I found yesterday that with the reverse I now have on the SX2P I can switch from forward to reverse without stopping in between which is useful when tapping. I am a bit hesitant though as I dont want to do any damage to the circuitry but I then thought is that any different than switching the 2.7 to reverse whilst its running forward. Obviously the tapping is using low revs and the mill seemed perfectly happy, it stopped and reversed just as the 2.7 does in your video. The 2.7 could of course have something built in for the change of direction which is probably a question for Ketan but just wanted to check that the switching is manual via the button.

Ron

Ron as soon as the SX2.7 goes into tapping mode it uses a different set up on the chip, Ketan has confirmed to my that the torque of the spindle is much increased using his scientific "Gauntlet" test and although the tap stops and reverses very quickly there is some ramp down and ramp up so as not to strain things.

For yours I would watch to see if the motor starts to get hot if doing more than one or two and also pause in the neutral position before going straight to reverse.

Also I'm not sure if your stop start using the speed control is the ideal way to be using the mill, I would need to check with Ketan whether you should have the speed set than use the on/off at the side. So tapping would be set a speed & direction - green on button - tap hole - red off button - change direction - green on reverse tap out - red off.

Thanks Jason, Ketan did tell me that the SX2P does have built in torque increase at low revs and I know that to be true as the mill has surprised me once or twice with decent power at low speed. I doubt it has the ramp up and down though as you have on your SX2.7 as mine doesnt have a built in tapping feature.

Out of interest why do you think it could be better to use the on/off for stop/start than using the speed control, if that proves to be the best way it is not a problem to use it that way.

tapping with the SX2P is easy if you have the R8 version as you can slacken off the quill, allowing the tap to thread and reverse under its own steam without binding.

Mine is a R8 and I have read about tapping with the collet loose but I dont like that idea at all and can only see damage to the collet and/or the location pin over time.

Ron