Thread cutting on the 260ATM

[jack620]

I cut my first thread today on my 260ATM. I turned the workpiece down to 18mm and set the tumblers for 2.5mm pitch. I offset the compound by 30 degrees, zeroed the crossfeed and fired her up. After the first pass it was obvious the pitch was much finer than 2.5mm.

I consulted the ToT and apparently there are two stud gears. The 18T is for pitches of 0.25-2mm and the 45T is for 1.25-5mm. After having a look under the hood I can see I've got the 18T stud gear engaged. That explains the finer pitch than I expected. The 45T gear is behind the 18T. What the ToT doesn't tell me is how to rearrange the gears to allow me to cut the bigger pitches. The 18T gear is engaged with an 80T gear which then engages the gear on the end of the norton box.

Does anyone have an idiot's guide to changing the gears on the 260ATM?

[pipeclay]

Not having a 260 this is probably no use,but have you described this correctly,it seems a bit strange.

On the Stud there should be only one gear not two as you have stated.

There is a gear on the Stud shaft but this gear is directly below your reverse tumblers,this gear remains where it is.

You will have an 80th idler gear attached to your banjo bracket.

There should be an 45 and 60 tooth gear on the screw shaft.

The 60 stays on the screw shaft and the 18 or 45 is used to make up the distance so that the screw shaft nut has something to bottom out against when it is done up.

To achieve what you require you would need to remove the 18 stud and the 45 screw and change them over,your train would then consist of 45 stud,driving 80 idler,driving 60 screw with the 18 acting as spacer on screw shaft.

[jack620]

Thanks pipeclay. My description was pretty poor. I took a photo and annotated it with the tooth count for the gears. Would you mind having a look at the photo and confirming for me which gears are swapped.
Cheers,
Chris

OK, disregard. You've explained it perfectly. Obviously the 80T moves on the banjo to accommodate the 45T stud. Is there a trick to getting the mesh of the gears correct?

[.RC.]

Image of what it should look like.. You swap the 18 and 45 around and loosen that square headed bolt and rotate the banjo to make the big gear fit..

So you

[pipeclay]

I generally just adjust by ear,if the mesh of the gears are to tight they will produce a lot of noise,the mesh in this case is adjusted with the idler,you require a little free movement of the idler between the stud and screw,if they are adjusted correctly you shouldnt hear them running when the halfnuts are not engaged.

When you get around to cutting the thread the slack in train will be tacken up by the load of cutting,this could produce a little gear noise.This noise will at times be drowned out by the backgears if they are engaged.

The same type of clearance should be kept when you are just using the feeds as well.

If you are having trouble adjusting the mesh you could try for around 1mm of clearance total,the clearance would be radial movement of the idler between the stud and screw gear.

Not much of a procedure,pretty much hit and miss but it works for me,but Im sure if theres a more detailed description in one of the numerous books available someone will let you know,then you can try and achieve the preffered clearances.

[jack620]

Thanks both.

How do you keep your gears so clean R.C.?

[pipeclay]

As a guess I would think that the gears may of possably been cleaned.
The gears require a type of lubrication.
I normally use chain lube for the open gears as it is quite sticky and dosent tend to be flung off.
For the Idler and reverse tumblers and other oil ports in the train I use 46 grade oil.

[jack620]

I've just been using the 46 grade hyd oil on the gears. I've got a can of Motul motorcycle chain oil. I'll give it a try.

[jack620]

Another question if I may:

If the thread pitches printed on the gearbox data plate are only valid when the correct gear is installed (18T or 45T), is the same also true of the feed numbers printed beneath the pitches?

[morrisman]

I've just been using the 46 grade hyd oil on the gears. I've got a can of Motul motorcycle chain oil. I'll give it a try.

Chainsaw bar oil works well . Mike

[pipeclay]

Yes it is true also,but if you wished to reduce or increase the feed rates stated it can be done by changing the gear size of the Stud or Screw gear with a different tooth count gear.

[jack620]

Thanks. I had a closer look at the pitch/feed chart. The max feed you can get with the 18T gear is 0.41mm. Seems high enough for most of the work I'm likely to do anyway.

[pipeclay]

If that is the feed rate that you would be using for most of your work,you maybe better off putting the 45 on the stud,that way if need you can get above .4.
Most users seem to chase the lower end of the feed scale,at least for sliding,cant remember off the top but I think surfacing feeds are either 1/4 or 1/3 of the surfacing rate.

[jack620]

No, I reckon I'll be using the lower feeds too. I'll save the 45T for when I need to cut a thread larger than 2mm.

Surfacing feed is 1/4 of longitudinal feed on the 260.