Inspect the parting tool closely before using. If using an indexable part-off tool, check that the cutting insert is in good condition. Figure 3: Video on how to properly sharpen and use HSS parting blades. Step 3: Maximize Cutting Tool Stiffness. Always maximize cutting tool stiffness by minimizing the length the blade sticks out beyond the toolholder block. For parting larger diameters or stronger workpieces, it will be necessary to adjust the stickout multiple times during the parting operation, as the tool cuts deeper into the material.
Figure 4: Minimize the distance the part-off blade sticks out of the toolholder to increase tool stiffness during parting. Note the clearance between the toolholder and the part is also minimized. The blade should be adjusted shorter. Figure 6: To adjust the part-off blade length for a particular cutting depth, use an Allen wrench to loosen the screw in the back of toolholder which loosens the wedge at the front of the toolholder and allows the part-off blade to be repositioned at a different length.
Figure 7: It is better to perform part-off operations closer to the chuck right because of the decreased deflection when parting. Step 4: Align Part-off Tool. To function, the part-off tool must be perfectly aligned with the X-axis on the lathe.
This can be done several ways; the most common two are using a block or a dial indicator, as shown in Figure 8.
Figure 8: To ensure the parting tool is perpendicular to the face of the chuck you can use a block whose surfaces are ground to be parallel to one another. Loosen the tool post, align the edge of the toolholder flush with the block, and re-tighten the tool post. Be careful to not drop the block. The carbide tip brazed onto these blades is more wear resistant than high-speed steel. A carbide tip brazed onto a ground steel shank makes these tools more wear resistant than high-speed steel tools.
Cut Type. For Use On. Cut Direction. Overall Length. Groove Width. Shank Height. End Shape. Shank Width. For Insert Thickness. Material Grade. Lead Angle. Maximum Depth of Cut.
If you do not usually use cutting fluid this has to be an exception. It is often easy to see the difference in cutting with fluid and without. Just for this reason it is worth always parting with the cutter in the upright position. It often helps things if the workpiece is supported from the tailstock — however little of it sticks out of the chuck. When the cut first starts this makes everything more rigid. But as the cut proceeds the cut reduces the rigidity of the work piece.
Near the end of the cut the presence of the tailstock reduces the tendency of vibration but because of the small amount of the material in the cut, the work piece is no longer rigid. This means the situation is roughly a work piece sticking out of the chuck and unsupported at the point where the cutting is happening. This means that though the tailstock will make parting off easier it does not mean that parting off can take place very far from the chuck where the real continuous support is.
So far the only point it is safe to part off is at a short distance from the chuck. But there is a way round this. It is to use a fixed steady. If a fixed steady is used to support the work piece it is possible to safely part off at any point on the workpiece so long as the fixed steady is just to the left of where the parting is being done. This arrangement is very useful when a large number of parts need to be made from a bar that is too big to fit into the spindle in the headstock.
The bar if fitted in the chuck. The fixed steady is moved just to the left of where the workpiece will be parted off. Once this has been done the steady can be moved to the left exposing enough material for the next part to be made. When doing this it is not essential that the steady is set up perfectly. It might be that the bar is not perfectly parallel to the axis of the spindle so the outside of it will need to be machined all over.
There is a special parting tool holder made by Jones and Shipman that is frequently encountered at auctions etc. Its key feature is that it is cranked so that the cutter is at 45 degree on the right, to the shank. All parting has to be done with the cutter at right angles to the workpiece. This means that when this tool holder is being used the shank must be at 45 degrees to the left. The only way this happens is when the lathe is fitted with an American style toolpost. The main difficulty with parting off with HSS blades is that, on occasion, the tool snatches and this can lead to a very unpleasant situation.
Very often when it is just about to snatch the lathe strains and the noise is the warning. Sometimes withdrawing the tool is most effective but sometimes the cutter gets stuck in the gap. Other times stopping the machine seems to be most effective. If the cutter gets caught in the gap one way of releasing it is to release the tool from the tool holder.
This usually happens with larger diameter workpieces, say, more than 25 mm diameter. The best way of avoiding this is to use a carbide parting tool. It is sometimes suggested that there are advantages in using a parting tool in the front toolpost but the wrong way up. The main advantage is that the swarf falls down more easily and does not clog up the cut. On the other hand the operator cannot see the swarf. Being able to see the swarf is a real advantage in that whether the cutter is cutting properly on not can easily be seen from the nature of the swarf.
But this is most often cured by applying cutting fluid. And this is most easily done with the cutter the right way up.
There are two ways of doing this. The tool can be upside-down and the workpiece rotates in the usual direction. Alternatively the tool is the right way up and the workpiece is rotated backwards. It is said that since the workpiece is pushing the tool down rather than up the whole set-up is more rigid. In normal turning its use is limited because if the cutter is mounted normally is will be opposite the parting tool when the topslide is withdrawn to the right.
If this cutter moves to the left the parting tool will move away from where the parting normally happens. The only time when this does not happen is when the lathe is being used as a capstan lathe. It is usual to use a rear parting tool on a capstan lathe but, in this case, all the machining is done from the capstan and though there might be one tool on the front of the cross-slide it will be almost opposite to the parting tool because the topslide will not be in use.
This also has the advantage of having a commonly used tool permanently in position. This is particularly useful when using the capstan.
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