Advice for surface finishing

[Ron LadenParticipant @ronladen17547]

Stuart,

Does your insert holder take DC## type inserts, maybe you know it does but worth a check.

My left and right holders from ARC take the CCMT and GT inserts and I have found those to be excellent and good pricing to, but I dont think they carry DC## inserts.

Ron

[Dave HalfordParticipant @davehalford22513]

The last number gives you the tip radius

02 finishing

04 middle of the road

08 roughing

Save your coated ones for really hard steels or hard spots in cast iron.

I've seen lots of photos of some cheap inserts with lumpy edges, these just need to go in the bin.

[Howard LewisParticipant @howardlewis46836]

FWIW,

You may get a better finish using a HSS tool, with a small radius stoned on the edge.

The larger the radius, the greater the risk of chatter, so you have to find a balance between speed, depth of cut and feed rate that suits the material, tool and machine in use.

Obviously the tool needs to be sharp.

Carbide tips tend not to be sharp. The intention is that when run at high speed the tool rubs and generates heat which softens the material.

Having said that, I have produced a good finish with a carbide tip by running at low speed with a very shallow depth of cut, with neat cutting oil applied.

Possibly the good finish is the result of burnishing rather than actual cutting.

It goes without saying that the tool must be mounted on the centreline of the work.

If you have a Tangential Turning Tool the standard HSS toolbit supplied has a radius on the edge.

For a finishing cut, a minimal depth of cut may be beneficial, (as Jason's 0.001" cut ), and the feed rate needs to be low. (You are effectively cutting a screw thread of minimal depth and pitch. The finishing cut should remove the "thread" left by the roughing cut

HTH

Howard

[HillclimberParticipant @hillclimber]

Posted by Stuart Cox 3 on 19/01/2021 19:45:33:

I used a brand new cutting tip and had the lathe speed at around 700rpm.

I have never managed to achieve a good finish with carbide tips on my S7, and assuredly not at that speed. My solution is, as others have suggested, HSS. But my preferred weapon is then the AR Warner HSS insert, which I can exchange with carbide.

Sadly, these are not available in the UK as far as I know? But can be ordered from….

https://littlemachineshop.com/products/product_view.php?ProductID=3575&category=-1550042347

Happily, they last well and I have been able to dress them with a stone when blunted.

Cheers, Colin

[chris stephensParticipant @chrisstephens63393]

For a really fine cut finish there is little to beat a shear tool and counter intuitively cutting in reverse direction. Cuts in the tenths of thou range are entirely feasible, and obviously that means they cut cleanly which helps the finish even on awkward metals.

For a really good appearance, roller burnishing is hard to beat and there are several videos on the net to demonstrate the process, i in fact have one myself showing a very simple set up.

[Ian Johnson 1Participant @ianjohnson1]

For added info on the DCMT tips, I use them to avoid grinding HSS (too messy and noisy!) But another reason is that the 55 degree point allows the tool to get really close to a revolving centre for machining small diameters.

I also get mine from JB cutting tools, mainly from their stands at steam fairs and bike shows, shame there wasn't any shows last year! Hopefully see them this year?

IanJ

[Author]

Posts