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Advice for surface finishing

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Ady120/01/2021 09:29:53
4220 forum posts
591 photos

A bit of green grit paper and less time than it takes to read this thread

old Al20/01/2021 09:41:07
180 forum posts

Thats a long piece of unsupported material thats been turned whatever grade it it.When you turned it, did you have a centre in it.

You cant just throw money at a problem thinking it will sort your problem out. Start with the basics. Thinking doesnt cost anything(unless you get it wrong)

Stuart Cox 320/01/2021 10:05:05
107 forum posts
17 photos
Posted by Martin Connelly on 20/01/2021 08:50:03:

I have bought them from JB Cutting Tools. I came across them because other people on this forum said they used JB and were happy with their offerings.

Martin C

PS I would just add that when you get inserts in boxes of ten as opposed to singles often they have a chart on the back of the box detailing their recommended depths of cut, feeds and speeds for various materials. It is probably worth looking at these for whatever you get and try to work with them. Also RPM is often a maximum not a recommended value.

Edited By Martin Connelly on 20/01/2021 08:58:06

Thanks Martin

Stuart Cox 320/01/2021 10:05:37
107 forum posts
17 photos
Posted by JasonB on 20/01/2021 09:18:50:

If it is the DCGT type you need then the one I'm using in that video is from APT, and is the DCMT 070202 which has a smaller tip radius than Ian's and is the one on the right of the second row. The price is for a pack of two for hobby use.

If you go to the full pack section then that gives speeds for the inserts but as industry won't be using them on steel you will only find ali and non ferrous speeds

Thanks Jason

Ron Laden20/01/2021 10:09:53
2122 forum posts
425 photos


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.


Dave Halford20/01/2021 10:24:19
1273 forum posts
12 photos

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 Lewis20/01/2021 12:53:17
4397 forum posts
4 photos


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



Hillclimber20/01/2021 14:46:30
176 forum posts
38 photos
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....

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

Cheers, Colin

chris stephens20/01/2021 15:41:41
1048 forum posts
1 photos

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 120/01/2021 19:45:03
334 forum posts
92 photos

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?


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