Hi all.
Bogs is back with a series of Top Tips to build your workshop machining skills.
As some of you may know I have had some serious family health issues to face over the last few months. I am glad to report that for the moment things are looking a little better but it has meant that I have been unable to contribute in the way that I had hoped to John’s website.
John has tried to keep my section of this site up and running for me and has added a few odds and ends into the Bog’s area, to try and keep things interesting for our regular visitors.
Circumstances continue to prevent me from writing long descriptions at this time, so in agreement with John, I will be digging into my fund of archive material, accumulated from my postings on various sites over the years. I hope you find this material of interest and, more importantly, helpful in developing your machining skills.
anyway, enough of all that, so lets get one of the most basic procedures sorted.
SETTING THE CORRECT CENTRE HEIGHT FOR YOUR LATHE TOOLING
John has already shown various ways to do this operation, all good, but unfortunately things have changed over the last couple of years on the amateur machining front, and a new method was adopted by myself to cope with it, and it will be shown later on in the post why I went this way.
If I came to a lathe where I didn’t have any setup tools, I would use the old ruler trick.
Gently trap the ruler between the tip of the cutter and the job, and these are the results you will get.
click on image to enlarge
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- Cutter height is set too low
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- Cutter height is set too high
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- Cutter height now set correctly
Adjust the height of your cutter until the ruler is standing perfectly vertical, as in the last picture, and you won’t be far off correct for cutting.
As far as I am concerned, getting the right tool height is one of the most important parts when setting up for cutting.
This sketch shows what happens in the three modes you can be in.
NOW ON TO THE METHOD I NOW USE
The very first thing you need to do is to get a very sharp end facing tool to spot on centre height. The reason you do it on the end, is that it will allow you to set the cutter very low and it will still give a decent cut.
remember, you can see a larger image by clicking on each picture
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- Raise the cutter slightly, it does help if you use a QCTP, and you will see the pip in the centre getting smaller.
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- Carry on doing this in very gentle steps until you have it spot on centre.
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- If you go too high, drop the tool again and start from scratch. If you do this correctly, and get the height spot on, you will never have to do this again.
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- What is needed now is something that will stand on end and be very stable. I used an old home made DTI stand, but a piece of largish tube that has one end faced square, or even an old square could be used. I blued this up so that it could be seen better for this posting.
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- By resting this tool on your cleaned off cross slide, you should be able to swipe a line onto it by dragging it across your very carefully set tool. Make sure you keep it pushed down and steady as you do it. That is your setting tool made.
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- Now whenever you want to set the height of a tool or check one that is in say a tool holder, you just pop your setting tool onto the cross slide, and bring the tool so that the tip ‘splits the line’. For the average person, splitting the line should easily get you within 0.001” of the required height.
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- Now this bit will explain why I have gone to this method. A few replaceable tipped tools now come with a negative top rake. This is how the tool is supposed to be and is designed to work in that orientation.
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- Unfortunately this type of tool is very difficult to set up using the old techniques of height gauges etc. but the method described above overcomes this difficulty.
While serving my apprenticeship I was taught to centre the tool from the centre in the tailstock.
I have bought three sets of cheaper feeler gauges and dismantled them, absolutely invalubale to have marked shims for setting too heights. I also use Meccano 5 hole strips as shims when i want bulk!
Hi John.
Tool Height.
Gauges are a very good way of setting tool height, you make one and have it for life of the lathe.
The way I used to teach my students how to set tool height albeit my twenty lathes all had Dixon QC tool posts.
1) Put a very pointed tailstock centre in the tailstock and adjust the tool so the cutting edge is right on the point.
2) If you have to use shims, then still put a centre in the tailstock
and shim up the tool for centre height. Having done this you can then with the point of the cutter scribe a mark on the tailstock barrel end.
Some of the old lathe used to come with this mark already on the tailstock, you then always have a centre height setting mark.
A quick check of tool height I used to show my students who were always complaining they had a blunt tool, with your bar stock in the chuck and your tool on centre height, take a 12 inch rule and place between the side of your bar stock and your cutting tool at about half way,just pinch so the rule stays upright, if the rule points backwards it’s to high,if the rule points outwards it’s to low veiwed from the tailstock end, you can get very accurate this way once you got used to it but it is only a rough guide, you probaly wind up with a little pip at the most.
The guy I bought my lathe off (Hobbymat MD65)showed me to rest the tool on the cross slide bed, which is also the resting base for the tool, and shim it up if necessary so the cutting point touched the point on the live centre.
But I guess all lathes are different.
What a great idea and so obvious once seen. I can put my 6″ rule back to the use it was intended for now!
Hi Widey (hope I got that right !)
Glad you found soothing useful. I faced off a short piece of 1 1/2″ Ali tube and scribed a line around the circumference in the lathe at centre height.
John