|42 forum posts|
This is my 1st proper Lathe and have a couple of simple (i hope) questions.
How do I know if its set for metric or imperial - ? I look at the little table on the front of the machine which shows all the pitch sizes for metric, but when I look inside the cover where the gears are they don't tally up with the chart.
Do the large gears inside the cover have any bearing on the lead screw gearbox.
Theres also a chart on the inside of the gear box cover with what looks like imperial pitches.
I'm still waiting on a manual for the machine but trying to work out whats what is a little daunting at the moment.
If i get my head around the gears and the screw cutting box I will be a happy man.
Thanks in anticipation.
|larry phelan 1||29/10/2020 16:10:04|
|866 forum posts|
Fear not !! Help is at hand, or not too far away .
Answers are being drafted even as I type.
Sorry I cannot help ,but there,s others out there who can, so hang in there !!
6440 forum posts
Can put some photos up Steve? Headstock, front gearbox, and whatever tables are available. Click this link for this forums photo HowTo.
The photos will probably contain enough clues for a forum member to suss it out.
Also possible to do it yourself from first principles. Put a rod in the chuck and arrange a knife or felt-tip pen in the tool-post so it just scratches or marks the rod. (Metal, plastic, wood, whatever, about 25mm dia so you can see it). Engage the gearbox to cut a thread and turn the chuck several times by hand to draw a spiral on the rod at least an inch long. (Quicker and easier to do with coarse threads than fine ones!) Then measure how many turns fit in one inch with a rule. If the lathe is set for imperial there should be an exact whole number of turns between the inch marks. A spiral that doesn't fit exactly inside an inch strongly suggests the lathe is set up to cut metric pitches. Repeat the test with a couple of different gearbox settings to confirm. Necessary because a few metric threads are close to imperial.
If not tpi, measure the distance between two turns in millimeters. Then loolk them up in a table. For example the threads on an ordinary M10 bolt should be 1.5mm apart, ie M10x1.5pitch. M12 coarse threads are about 1.75mm, and M6 are 1mm apart.
Once the spiral is identified it should be possible to relate it to the gear setting tables, and it should make sense.
|norm norton||29/10/2020 17:26:07|
|138 forum posts|
The 140 is a metric lathe, with a metric leadscrew. The gearbox will give metric screwthread pitches using the set of 'big' gears described in the manual. Register on this Harrison Forum where there are manuals, etc. With a special set of 'big' gears you can cut exact imperial pitches, but the leadscrew has to stay engaged.
I have a 140 and have sorted out the imperial gear set so ask me if you can't find it on the Harrison forum.
p.s. it is a superb lathe to use so you have done well to get one.
Edited By norm norton on 29/10/2020 17:29:49
|42 forum posts|
Thanks for all the input - the lathe was brought from a guy who inherited it but knows nothing of it. He did say that he remembers the user of the lathe did lots of work on traction engines.
My issue is that when I look in the main gear housing the drive gears don't match up with the chart on the front lead screw box. It also has a lead screw dial attached to the side of the saddle. Which to a beginner like me implies its for imperial threads.
I will 99% of the time would want it to be metric so would want help to make sure it is.
Thanks for the tip - I will have a look at the Harrison forum.
|norm norton||30/10/2020 10:13:13|
|138 forum posts|
Lead screw dial will tell you when the metric screw cutting can be re-engaged.
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