Myford 7 303SS Feeds & Speeds

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Myford 7 303SS Feeds & Speeds

This topic has 13 replies, 10 voices, and was last updated 18 January 2017 at 12:14 by Neil Lickfold.

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15 January 2017 at 22:37 #15902
Oliver Webster
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@oliverwebster17169
Myford 7 303SS Feeds & Speeds
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15 January 2017 at 22:37 #278043
Oliver Webster
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@oliverwebster17169
Looking for a bit of advice on feeds and speeds for a project I’m working on. I’m turning a 1″ 303 round bar down to 3/4″ diameter in a couple of places. I’m using carbide indexable tooling (DCMT07). Some googling got me some figures to start with which are 570SFM at 2,100RPM with a .004″/rev feed and .040″ depth of cut (taken from a site about mini lathes). My 7 seems totally unable to manage that DOC with these other values so I’ve been taking lighter cuts. I started at .020″ but that didn’t work as there appears to be too much flex and I end up with a taper. So now I’m running about .010-.015″ and getting red hot swarf. My next step would be to reduce the spindle speed, but I’m interested to get some idea what DOC, feeds and SFM other myford users are operating at. Very grateful for any help.
15 January 2017 at 22:39 #278044
John Haine
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@johnhaine32865
Much too fast!!!!! Try 800 rpm.
15 January 2017 at 23:08 #278055
Allan B
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@allanb
Agree with the too fast, but I would be tempted by as slow as 400-600rpm
15 January 2017 at 23:17 #278059
Oliver Webster
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@oliverwebster17169
What kind of feed a DOC are you guys running for roughing and finishing? I was using .004/rev for roughing and .002/rev for finishing. Finishing cuts have been really light, maybe .005″ DOC. This is me just starting to rough things so not sure where to start. .010-.015″ seems reasonable but others are talking about taking 3x or 4x as deep…
15 January 2017 at 23:51 #278064
Allan B
Participant
@allanb
I would have to check my charts for feed speeds, I only tend to know rough rpm’s off the top of my head
15 January 2017 at 23:57 #278065
Anonymous
You may find the first and second posts in this thread interesting:

**LINK**

From what I've learnt since I wrote these notes I'd now be roughing at 8-10thou/rev and finish at 4 thou/rev. I almost never use the feeds below 4 thou/rev.

When looking at DOC and feeds bear in mind that they're for a bigger lathe with several hp to play with.

Andrew
16 January 2017 at 00:57 #278067
duncan webster 1
Participant
@duncanwebster1
I'd use HSS, you can get it sharper hence less load. Tool life is shorter, and you'll need to run at 250-300 rpm, but if you were in a hurry you wouldn't be using an ML7. Follow advice above on feed rate if you let it rub you're lost. I find my Eccentric Engineering tangential tool thing great on SS.

Watch out for the swarf, it comes off in long very sharp spiral when you get it right. Rips your hands to shreds. Don't ask how I know.
16 January 2017 at 07:55 #278082
bricky
Participant
@bricky
I use infeed of 15-20th and seldom unless turning brass or bronze go above 600rpm .I use tipped tools for roughing and finish with HSS in a tangential holder .I have a S7.

Frank
16 January 2017 at 11:50 #278144
Oliver Webster
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@oliverwebster17169
Thanks for the feedback folks. As I said – first step in my own head is to reduce the spindle speed. Upon considering it a bit more last night the 570 SPM quoted by Sandvik (the insert manufacturer) will be based on flood coolant I bet, so it would make sense that it's running too fast.

That link to the other thread was very useful. Seems like the .004"/Rev feed is probably about right. I won't be able to match the .040" depth of cut – my machine just doesn't seem up to that much, but if other people are taking around .015-.020" that's about where I was machinig mild steel so I'll stick with that. I've been doing a finishing cut using a round insert at .002" depth at 2,100 RPM. The finish is very good so I'll probably stick with that but reduce the RPM to 800 for roughing cuts.

Will try all of the above this evening. Thanks all.
18 January 2017 at 09:05 #278548
Ian S C
Participant
@iansc
Speed, if in doubt start slow, and work up.

Ian S C
18 January 2017 at 09:19 #278553
Jon Gibbs
Participant
@jongibbs59756
Cobalt HSS (either M35 or M42) offers a big advantage over normal M2 for SS in my experience. Much better tool life.

+1 for a tangential tool holder.

Jon
18 January 2017 at 10:29 #278567
Nigel Bennett
Participant
@nigelbennett69913
My first thought is that to achieve the speeds and feeds the OP's Google search produced, you're looking at a big new CNC machine with flood coolant.

With a light hobby lathe like the Myford 7 series, it's a case of adapting the figures to what the machine can physically do. The condition of the slides and headstock bearings can seriously affect metal removing ability – as can the horse-power of the motor.

The amusing article about turning by Michael Oxley in the Christmas issue of ME in the early 1950's is quite relevant here.. It went something like "Twiddle the knobs… twiddle all the knobs in sight…if the metal starts coming off in huge red-hot chunks, ease back a bit…"

So essentially it's up to you to find the limits of your machine (by just going past the limit!) and reducing either the speed or the feed and/or increasing the supply of coolant. And use sharp tools! The DCMT07 tip isn't sharp – it is really much more suitable for BIG machines – say a Colchester Bantam and up. It might be better to try the sharp DCGT07 grade (JB Cutting tools can supply – usual disclaimer). I find that although relatively fragile, they produce really good finishes and I use them a lot, even for materials they aren't' "supposed " to be used for.
18 January 2017 at 12:14 #278585
Neil Lickfold
Participant
@neillickfold44316
All the book data is based usually on flood coolant and an insert edge life of 15 to 25 mins. Of course a production machine is going to be taking away a lot of chips at that rate. Stainless is often quite a high feed rate. There are stainless specific inserts to by with special coating and a cutting geometry to make it chip. On a home machine, I by the finishing inserts and don't run my spindle any more that the fastest position on the low speed main pulley. I no longer use the high speed main pulley. I went with the DCMT11T3 series of inserts and holder, due to the large availability of different inserts, and because the company I mainly buy from for home, does sell in small insert quantities. The depth of cut and feed rate is machine and material dependent. So take cuts deep enough that you can get good chipping and a feed rate that makes it chip. I would think that if you had a insert with a 0.2mm radius and a DOC of 0.5mm with a good coolant, will be able cut at 0.1mm per rev no trouble maybe higher. With stainless and Ti material, the coolants for those materials , have high pressure additives that aid in the sharing and deformation of the material. On small lathes, the larger radius inserts seem to load up the machine more, so my common radius choices are 0.2mm for steel and 0.4mm for Ali. I would use about 300 to 400 rpm with coolant.

Neil
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