tips to get best surface finish

The finishing cut is the last step before a part reaches inspection, and after all the time and effort that goes into making a precision part, it is critical that this final step produces a quality surface finish. Incorporating a few key practices can help prevent the need to scrap parts in this last stage and ensure your surface finishes are always up to snuff.

The surface finish can often be improved by using a higher cutting speed

The insert geometry (neutral, positive and negative rake angles, as well as positive clearance angles) influences the surface finish The selection of insert grade has some influence on surface finish In the event of vibration tendencies, select a smaller nose radius.

Wiper insert

Wiper inserts are capable of turning components at high feed rates – without losing the capability for generating good surface finishes or chip-breaking ability.

A general guideline is: Two times the feed-rate, same surface finish. Same feed-rate, twice as good surface finish.

Wiper inserts are designed to smooth the surface generated as the insert is fed along the workpiece, the wiper effect is primarily designed for straight-line turning and facing.

Use the Right Feeds and Speeds

It’s absolutely critical to have the right feeds and speeds for finishing work–no guessing!

Clear the Chips!

Chips down in the work will scratch it up as your cutter slides them around in the hole. With work hardening materials like stainless, you may as well scatter a handful of hardened steel chips to scratch up your work.

Use the Most Rigid Possible Workholding:

Rigidity in all areas is key to a fine surface finish and any vibration of flex is going to be bad for your surface finish.

The primary impact of workholding on surface finish is vibration. In the worst case vibration will turn into chatter, which is a harmonic effect that will be very visible in your surface finish. Clearly, the more solid you can make your workholding, the less likelihood of vibration there will be.

Make sure your workpiece is supported and clamped over as much area as possible surrounding the cut while still leaving room for the cutter to get in there and do its job. Remember that as you are removing material during the machining process, you are in some sense weakening the workpiece. You may weaken it to the extent that the vise or other workholding fixtures can start to deform the part.

For example, suppose you’ve firmly clamped a relatively thin piece of aluminum plate flat in the vise. You intend to machine away the middle so it’s like a picture frame. The initial slotting pass may relieve enough material that the slot pinches against the cutter with poor results.

Use Different Tools for Roughing and Finishing

Don’t finish with the same tool you used for roughing. Keep brand new sharp tools for finish passes and rotate them to roughing work after they’ve done a brief tour finishing. If you’re using an indexable tool, like a face mill, use two different sets of inserts.

Minimize Deflection and Chatter, Maximize Tool Rigidity

You can’t get good surface finish if your tool is deflecting excessively or chattering. You’ll see every bit of that in the finish on the cut sidewalls.

Use Balanced Tooling to Reduce Vibration

Another way to reduce vibration is to use balanced tooling. The higher the rpms, the more important this can be.

Surface Finish With Facemills

Facemills are a staple for most shops. They’re great for squaring blocks and facing large areas.

 

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