Correct Lathe Cutter Setup

by macarina

126K13316

Intro: Correct Lathe Cutter Setup

Using a Lathe is one of the first skills learned by a beginning Machinist. There are a lot of tips and tricks that are not readily available to everybody. Here is one simple trick that is fundamental to getting a part properly turned. Setting the outside cutter to the proper height is something rather elusive to a good many aspiring lathe users.

Not having the cutter at the right height can damage your part, tool, lathe or even injure someone.

Observe all the rules and procedures you were taught while taking the Lathe SBU classes.

I made it at TechShop Chandler, techshop.ws.

STEP 1: Get the Right Tool

All the Setup steps are done with the lathe powered off. Make sure there is no chance of accidentally turning on the machine.

All is needed is a simple metallic ruler, about 6 inches long. They are only a couple of dollars. They are available at any hardware store or home improvement chain in the measuring tool isle. In a pinch any metallic straight flat "Ruler-Like" object would do.

STEP 2: Chuck Your Part

Load the cylindrical part in your lathe. Here is an extra tip: as you tighten the chuck rotate the part with your hand lightly, as the friction just grips the part, keep tightening with the key, until it does not move any more. This helps centering the part and gives a truer alignment along the axis of the lathe spindle. It will be less wobbly as it turns...Also it will be less waste as the truing cut taken is less.

Get the part cinched down good and tight.

STEP 3: Load Cuter Tool

Install a regular cutting bit in the tool post. Make sure it is the tool that you intend to use for your first cut. This tool height procedure needs to be repeated for every tool that will be used in outside turning. Install the tool tight in the holder and set the holder perpendicular to the part. Make sure the tool seat is clean of debris otherwise you will get a false setup that is not repeatable. See the pictures above.

STEP 4: Set Ruller in Position

Lock the cam on the tool post

Bring the lathe Carriage close to the chuck end of lathe and using the cross feed wheel get the tool closer to the part until you can pinch the ruler against the part to be turned. Do not tighten too much as you will damage the ruler. Just tight enough so that the ruler does not fall off and stays pinched between the tool and the surface of the part.

STEP 5: Reading the Ruler

If the tool height is set correctly, the ruler will be absolutely vertical. Just as in the first picture.

If the ruler is tilting to the right then the cutter is sitting too low. Release tool post cam and Adjust the height wheel on the tool post to get it to the right height. See second picture

If the ruler is tilted to the left toward the back of the lathe the tip of the cutter is above the center line of the part. Release cam, and Again spin the knurled wheel in order to drop the tool just slightly.

Adjusting might take a few tries until the ruler is apparently straight up and down (vertical) as viewed from the back of the lathe. In time the operator will develop a real knack for setting the tool straight in just one or two tries.

If the ruler is vertical, set tight the locking nut sitting over the adjusting knurled wheel. Your setting will be preserved

STEP 6: Take First Test Cut

Release cam and remove cutter. Install it again longitudinally along the lathe axis, and flip it around to take a facing cut. Take a light facing cut. If the tool is not exactly on center it will leave a little nib on the part, see photo.

As you are watching the tool cutting, you should be able to see if the nib is left because the tool is too low or too high. Stop lathe, Back off the carriage and repeate the above steps. Use small increments while adjusting the Knurled wheel on the tool holder.

The perfect setup will create a facing cut smooth and without any imperfections. See second picture

STEP 7: Final Adjustments

If you wanted to take a facing cut only, then you are done, if not and you need to turn a part along its axis, you need to take the tool out and set it up again perpendicular to the part. The set nut will not allow the tool to move so your hard work setting it all up will be preserved. The setup is now repeatable. Make sure all the surfaces are clean...

Do this for all the tools that you plan to use turning your part. It is useful to have multiple holders that once set can be just dropped in place.

This procedure should be followed any time there is a tool change done.

Having several holders with the tools already set at the right height will save you time. The picture above illustrates a perfectly turned part that is about to be milled.

Hope this help, Happy Turning

12 Comments

al omran 6 years ago

what are the reasons that make my lathe machine do not give me right measurment

AndrewG308 7 years ago

This seems to be one of the easiest methods I've run across for setup!

AllisonC64 7 years ago

Does anyone the actual time it took to set-up?

TurnerT 9 years ago

Even as a machinist trying to troubleshoot this gave me a great little trick to add to my knowledge cheers

CementTruck 9 years ago

That makes so much sense. Thank you.

Any tips on how to align an internal (i.e. boring bar)?

macarina 9 years ago

I am not a machinist by trade :) These guys are all but extinct. However I am formally trained in manual machining and other metalworking since I was about 12. In Europe, where I grew up, that was pretty much mandatory for boys and sometimes girls too. After moving to the USA I got to train as a CNC machinist and can program and operate just about any CNC Mill, Lathe or Mill-Turn up to 5 axes. I did this in my spare time for fun. Unfortunately there is not too much money to be earned in this trade on a steady basis, and that is why manufacturing has moved elsewhere. I do not mind share any of my knowledge, all I know is because of nice people that did not mind answering my questions. I own two small lathes but never used them for much. I have access to good industrial machines any time so all I need to provide, is some custom tooling if I want something out of the ordinary. I make different parts and pieces for myself and friends. Metalworking is just one of my interests. I also work wood, electronics, blacksmithing, automotive and just about anything that I think is interesting or challenging.
Cheers, MAC

macarina 9 years ago

Boring bars are aligned the same way, just pinch the straight ruler to the opposite side of a cylinder. Some boring bars are set slightly below the center line, but that depends on the manufacturer and how the cut looks like after a few cuts. The look and feel of the "cut" can give clues as to how the "cutter" is performing. Sometimes the play in the various moving parts of a lathe can alter the precise set up done while the whole lathe is stationary. It does take some experience to "read" the results. Unfortunately a lot of home machinists do not have the luxury to have a pro by their side and give feedback, so there is nothing to use for comparison...

CementTruck 9 years ago

Are you a machinist by trade or a metalworking hobbyist? Do you mind if I pick your brain from time to time?

I picked up an ancient Smithy AT300 (barely used) last year, did some upgrades and sold it and bought a used Smithy Midas 1220 LTD with all the bells and whistles (for almost the same price I sold the AT300 for). I know Smithy's are an exercise in compromise but that's what I could afford. Still working on acquiring/manufacturing tooling. Sooner or later maybe a Gunsmith's lathe is in my future. :D But for now I feel the LTD is a pretty capable machine that will serve my meager needs for years to come.



gglass 10 years ago

Quickest way. get extra tool holders. Keep all your most used tools in a locked holder then it's always centre.

or if you can just turn .1mm off the face with the tool. as close to the centre and adjust till no pip.

or get a tool spot on. then measure the distance from the slide to the tooltip. note down the measurement and then the next tool from then on you put in adjust to said size using the rule.

ironsmiter 10 years ago

another easy way is to use a center in the tailstock.
the top of the tool set at the some height as the point of the center.