Cutting a Groove – help needed

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Cutting a Groove – help needed

This topic has 18 replies, 10 voices, and was last updated 14 July 2010 at 01:56 by ZigFire.

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12 July 2010 at 03:28 #53314
ZigFire
Participant
@zigfire
Hi Everyone,

I have a round section of mild steel (100mm dia x 30mm long) that I need to cut a grove into the centre of the circumference 10mm wide by 15mm deep.

Now I tried using my parting tool but I could not get the rpm low enough and subsequently destroyed the tool (blade type with replaceable inserts, used plenty of lubricant).

Obviously I need to purchase a new cut off tool but didn’t want to risk another breakage.

My question is can this slot (groove), be cut on a vertical milling machine by securing this material in an indexer with the axis of the material horizontal and using an end mill cutter or slot cutter while rotating the job with the indexer?

This is a pretty deep slot for me and I am concerned there will not be enough rigidity if using the indexer.

Any advice greatly appreciated.

Cheers

Michael
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12 July 2010 at 03:28 #29417
ZigFire
Participant
@zigfire
12 July 2010 at 07:23 #53317
JasonB
Moderator
@jasonb
You would be better off with a rotary table in the mill and use say a 6mm cutter to reduce the load, an indexer will give you a facited bottom to the groove.

Another option would be a thinner parting tool say 1.5mm and go in either side of the groove again this will reduce the loading on the tool.

Whats the lowest speed you can get down to?

Jason
12 July 2010 at 08:49 #53318
ZigFire
Participant
@zigfire
Hello Jason,

I have a 300 mm rotary table and the job is just 100mm in diametre. As the job is only 30mm high the spindle of the mill and collet would not clear the vertically mounted table (unless I packed the job out from the table..just thought of that as I was typing).

My lathe can get down to just 66 rpm(single phase). The parting tool I was using was 2.2mm wide.

Is there a trick to the setting up the parting tool, ie should it be dead on centre height or just below?. I was thinking if it was just below centre it may tend to bite and “dig in”.

Cheers

Michael
12 July 2010 at 09:14 #53320
mick
Participant
@mick65121
Hi. Michael.

Slightly below is OK for a plain groove, also try supporting the end face with a presure pad, which only needs to be a smaller diameter piece of stock faced one end with a hole through it. This in turn is supported by the revolving back centre. The trick is not to over tighten the tail stock, as this may push the work piece off centre.
12 July 2010 at 10:41 #53324
Versaboss
Participant
@versaboss
Hi Michael,

difficult to say something without seeing what you did. But I think that there must be a fundamental problem somewhere. Imho a 2.2 mm inserted chip parting tool at 66 rpm should work a treat. Now let me consult my tables – yes just around 20 m/min (sorry for these newfangled measurements…well you used mm too!). Thats a perfect speed for HSS tooling; with carbide I think you could double the rpm.

Could it be that your stuff is not mild steel?

Greetings,
12 July 2010 at 10:41 #53325
Versaboss
Participant
@versaboss
Hi Michael,

difficult to say something without seeing what you did. But I think that there must be a fundamental problem somewhere. Imho a 2.2 mm inserted chip parting tool at 66 rpm should work a treat. Now let me consult my tables – yes just around 20 m/min (sorry for these newfangled measurements…well you used mm too!). Thats a perfect speed for HSS tooling; with carbide I think you could double the rpm.

Could it be that your stuff is not mild steel?

Greetings,
12 July 2010 at 11:20 #53329
Lawrie Alush-Jaggs
Participant
@lawriealush-jaggs50843
Hi Michael

There are several options available
You mention that the you cannot get the collet low enough to cut. I had the same problem several weeks ago when machining a circular slot 7.35mm wide x 25mm deep in a piece of 1045 that was 70mm square. I solved it by using long series 6mm four flute HSS end mill. I now have a quick change tool post.
My rotary table only has three slots so I had to make an adapter out of 16mm aluminium. As I required a centre hole in the block of steel I was able to use that to hold the work down. I then bolted two peices of steel to the aluminium plate at the base to hold the peice against the cutting force. You could perhaps adapt that slightly (quite a lot really!) to suit your round work.

You second option is to trepan the material in the lathe. You wont be successfull with a parting off tool, you need a correctly shaped trepaning tool. You can grind one up from HSS. See this video to get an excellent demonstration of the shape of the tool and it’s use.
http://www.youtube.com/watch?v=8bDIEwj6UW4&feature=related
The bit you are looking for is about eight minutes in. The next vid, number three
http://www.youtube.com/watch?v=AyrOtjjFoRs&feature=related shows the profile of the tool very well and is about 1.40 min in.
To make one up, take a compass and on a sheet of paper describe a circle of the inner and outer diameters you which to cut.
Grind a tool shaped to fit within those circles. You do need to be careful with your feed rate and do use plenty of lube.

The tool should be dead on centre and if you look at the shape of the tools in the videos you should get a good idea of the reliefs and rakes required

Lawrie

Edited By Lawrie Alush-Jaggs on 12/07/2010 11:22:51
12 July 2010 at 12:31 #53331
ZigFire
Participant
@zigfire
Posted by Versaboss on 12/07/2010 10:41:49:

But I think that there must be a fundamental problem somewhere. Imho a 2.2 mm inserted chip parting tool at 66 rpm should work a treat… Thats a perfect speed for HSS tooling; with carbide I think you could double the rpm.

Could it be that your stuff is not mild steel?

Greetings,

Hi Versaboss, thanks for the feedback, I think the fundamental problem is probably ME! Anyway your comments re speed are exactly what I though as well. The material is definitely MS. I had to bore 40mm hole for bearings and the material turns exactly as MS should.

The only other point I could make is due to the low profile of the job (30mm) I can only just get the first two teeth of the chuck jaws onto the material to allow clearance for the parting tool. So not much grip if the tool decides to bind. Perhaps I could move the job further into the chuck and cut halve the groove, then turn the job around to cut the other half and then take a final fine cut with the job just in the chuck to smooth out the bottom of the groove. Specs aren’t too critical for this one, I just don’t want to break another blade, they ain’t cheap..

Cheers

Michael
12 July 2010 at 13:55 #53334
Ramon Wilson
Participant
@ramonwilson3
Michael,

Just a thought but can you not make a plug for the 40mm bearing hole previously machined (assuming its concentric of course) and then use tailstock support. The rpm/tooling sounds okay as others have said but the dig in and blade loss is probably due to insufficient holding power for the dia given what you describe.

Also not driving the tool on full width very deep then retracting and moving over each side to widen the slot will aid relieving pressure as much as possible. Hope that’s not granny teaching.

Regards – Ramon
12 July 2010 at 14:45 #53335
Gone Away
Participant
@goneaway
Just curious – when you guys are talking about milling the groove using a rotary table how are you using the end-mill? I can see two possibilities:

1. Bring the end mill down on the top-centre of the part and cut using the end of the cutter, using the z-axis feed for depth of cut.

2. Bring the end mill down the side of the part, cut on the side of the cutter and use the x or y feeds for depth of cut.

I’m curious because I’ve considered doing this myself in the past and wondered which is the best approach.

Edited By Sid Herbage on 12/07/2010 14:46:26
12 July 2010 at 15:11 #53336
Lawrie Alush-Jaggs
Participant
@lawriealush-jaggs50843
Hi Michael

I have to confess to having missunderstoodd what you were trying to do when I answered you question. I thought you were trying to machine the face rather than the circumference.
In answer to your latest question though you can certainly mill the cut you need and you will get a better job for the depth you require.
If you mill on the side of the cutter using X and Y you will end up with a radius at the bottom of the cut and it will require a fairly long cutter to acheive the depth you want.
If you mill using the bottom of the cutter and the Z axis for feed you wil have to be on dead centre with the cutter and the rotary table otherwise you will end up with a dished bottom of cut.
Cutting using Z is better from the point of view of tool length though you are quite possibly going to end up with problems with collet holder clearing the jaws of the chuck – assuming you are using one. If you aren’t and are going to bolt directly to your rotary table you will most likely still have a problem given the diameter of your table.
Firstly. If you can drill the center of the peice you want to groove, then I would do that and superglue and bolt the peice to that and mount it in the chuck on your table. That will give you plenty of clearance. When you are done, just remove the bolt and give the disk a good whack with a soft face hammer, the glue can then be cut off with a razor blade.
If you don’t have a chuck, then turn up a morse taper with a stub protrusion to suit the RT, turn a thread on the end of it to take the disk, drill and thread the disk and screw it onto the MT.
If you can’t drill it, then I would mount it on the RT horizontally clamping it in two places in less than half the diameter and then cut just over half the circumference with a slitting saw. It will take you several passes to achieve both the Z and X depths you require and you will have to reclamp but it will get you there.

Lawrie
12 July 2010 at 19:07 #53340
KWIL
Participant
@kwil
With a blade mounted parting tool of say 3mm width, on mild steel, cut the two outer edges at or around 400rpm max, this assumes that the insert is a neutral one. ie not a left/right sided cutter and the tool is square-on to the cut and at the correct height. In this way the edges are supported by the wall. You then have to remove the centre piece. You may be able to do this, or at least most of it with the parting tool, depends upon the tool width. A blade type parting tool, which is flexible, should not be used as a profiler, ie, with right or left hand movement, there are special inserts and holders for that type of machining.

Edited By KWIL on 12/07/2010 19:09:52

Edited By KWIL on 12/07/2010 19:10:32
13 July 2010 at 00:25 #53345
ZigFire
Participant
@zigfire
Hey Guys, have to say I’m pretty impressed with the level of response here, thanks.

Lawrie, no probs on the misunderstanding, I thoroughly enjoyed watching the youtube links you posted. Amazing seeing the tooling cut the metal like butter. Thanks for all the in depth comment as well, very much appreciated.

For end milling I would be placing the job in a chuck and using a 10mm end mill and the Z axis only. Thanks for the tip on the dishing at the bottom of the groove, didn’t realise this could happen but makes perfect sense when you think about it.

Sid, I was looking at doing your Point 1. However the cut is to form a groove on the circumference not a shoulder, so I would have to plunge straight in using Z axis.

Ramon, thanks for the supporting tip. If I try the lathe again I could place the 40mm bearing into the job and use the dead centre to support the centre bearing cage and thus the job. As you mentioned I was probably a little ambitious doing full depth cuts to achieve the grove, so I will try a little at a time across the full width of the groove without cutting transversely as Kwil suggested as I do know the tools I have is not designed for this.

At the end of the day I guess it is slow and easy with a lot of support and lube. Anyway I have SIX of these to do so I will try all the suggestions mentioned. I’m no professional machinist that’s for sure, so I really appreciate the knowledge bank here, Thanks heaps guys!

Cheers Michael

Edited By ZigFire on 13/07/2010 00:26:27
13 July 2010 at 08:45 #53348
KWIL
Participant
@kwil
Micheal,

I am not suggesting a little at a time, I am more for the full depth cut at each extremity (in your 10mm case leaving two slots separated by say 4mm) and then removing the remaining centre piece.
13 July 2010 at 12:16 #53352
Ian S C
Participant
@iansc
I frequently do a similar job . On the machines I assist in building, a couple of 100mm pullys are required to take wire ropes, so I take an off cut of 100mm bar, bore it to take 40mm bearings, cut two rope grooves 7mm x7mm, then part it in two, fit the bearings, all OK. My lathe is a Taiwanese 1326 belt head, and 3mm wide HSS parting tool. I take two cuts just short of depth for the grooves, then after taking out most of the metal in between, I use a form tool to round the bottom. The chain sprockets we use on the machine are mainly profile cut from 10mm hot rolled plate(gas cut, not anything fancy like lazer, or water jet). I use my bottom back gear speed of 60rpm, and pleanty of lube. Ian S C

We only have a small production, about 10 per year max, about half of these have the pullys, maybe 30 machines.

I forgot this, after boring I place the lump of steel on a short mandril, and clamp it up with a big washer and it’s just held by the friction of the fit on the mandril and the washer.

Edited By Ian S C on 13/07/2010 12:21:28

Edited By Ian S C on 13/07/2010 12:31:27
13 July 2010 at 12:27 #53353
Versaboss
Participant
@versaboss
Kwil’s way is the way I would do it also. What would help with the gripping problem would be (in ascending order of benefit):

– 3-jaw chuck with soft jaws (bored out say 8 mm in that case)

– 4-jaw chuck

– 4-jaw chuck with soft jaws, as above

and tailstock support in each case.

Milling such a groove on a rotary table I would only consider if no lathe is aroundin 100 km distance. Thinking of it makes my few remaining hairs rise!

Greetings, Hansrudolf
13 July 2010 at 17:11 #53360
Bogstandard
Participant
@bogstandard
Will this post help you with what you are trying to do?

Recess

Bogs
14 July 2010 at 01:56 #53376
ZigFire
Participant
@zigfire
Thanks Bogs but I was trying to cut a groove into the circumference not the side of the job.

Anyway I received a new parting blade for my tips in the mail yesterday and thought I would give it another go. I did all the right things, got the speed as close as possible to recommended, parting tool blade protrusion as short as possible, job secured further into the chuck for more support plus plenty of lubricant. All this worked a treat, managed to cut the groove no problem, even used a slow power cross feed. Just had to turn the job around in the chuck to cut the other half of the groove due to the low job profile.

In retrospect I iwas probably feeding too fast and heavy handed the first time, the job was minimally held in the vice, the cutter dug in and bang! Live and learn eh!

Thanks for all your help again guys.

Cheers

Michael
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