Member postings for s d

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0.015” sounds WAY TOO MUCH … is that a typo ?

MichaelG.

Most makers that publish cutting data tend to show 1D to 1.5D on their 4-flute cutters so two passes at the most when also using the usually published 0.1D stepover.

It is possible to use more Ap (vertical) depth if the Ae (sideways) stepover is less particularly for the 5 or 6 flute finishing cutters.

Don't try the drill chuck

The irregular pattern would seem to suggest flexing somewhere rather than a regular pattern that could be attributed to runout.

Edited By JasonB on 05/07/2023 13:10:58

Ah, fair enough.

Do we know then, if the milling bit is true and regular ? - is it possible to check each flute "diameter" with a DTI? - perhaps one is slightly proud compared to the others.

In the same vein; does a DTI show any bend in the driving shaft, as measured against the side of the cutter as it is rotated through 360°.

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Edited By John Doe 2 on 05/07/2023 12:33:28

Anything that can be done to stiffen the process will help so if all the none moving axes are locked and the stick out of both the spindle in the head and the tool in the collet is reduced to the minimum then the next question is are you tightening the tool in the collet sufficiently to reduce flex. If you are not using a ball bearing ER nut and suitable wrenches to put high torque on the nut and therefore high pressure on the tool shank then the tool position may flex slightly in the collet holder.

Martin C

The plot thickens; it is not an issue with 316 but milling in general.

For a start there is too much stick out on the tool. The holder should be down to the top of the flutes. Given that there is significant cutting on the return pass something is moving that shouldn't be. I suspect the cutter is flexing for starters.

Andrew

Edited By Andrew Johnston on 05/07/2023 10:28:47

The 5mm could be run faster than the 10mm approx twice the speed if HSS and if it is carbide then your 2000rpm would be OK.

Out of interest is there any chatter which can often be heard as as squeal while cutting and what is the swarf coming off like? If very fine more dust like then you are not cutting, it should be nice chips.

Although this is just EN3 steel it should give you an idea of how things should sound and the chips produced, towards the end you can see how fast I'm turning the handwheel (2mm pitch screw) . This was a 10mm 4-flute HSS cutter at about 800rpm (25m/min) as it was mild steel

I'm not clear exactly which cutters from Arc are being used? I have not used their HSS cutters, but have tried their premium carbide endmills and was impressed.

The cutting parameters should be fine, but I suspect the mill column isn't stiff enough. Of course HSS cutters are less stiff than carbide so the cutter itself might be flexing as well.

Andrew

As Andrew says 2000rpm is fast for an HSS cutter, even if it were OK you would have needed to be feeding at a minimum of 200mm/min to avoid the cutter rubbing (0.025mm chip load). Once the cutter starts to rub you can start to loose the edge and also risk work hardening so cutters could now not be at their best.

It would be worth checking that he spindle bearings are not too loose, usually a nut and locknut at the top that will take up any play. Also lock all the other axis except the one you ar eusing to feed with

Of the austenitic stainless steels 303 and 316 machine very well, but for some reason 304 is a pig. It is possible to get a good finish on 316. However I can see a number of potential issues.

First what is the provenance of the cutters, manufacturer and supplier?

For a 10mm HSS cutter 2000rpm is way too fast, should be more like 500rpm, and that's based on recommended speeds for industry.

Work hardening is a real problem with 316. Taking a relatively shallow depth of cut means you need to feed faster than one might expect due to chip thinning.

The play in the column seems excessive to me.

I suspect the mill simply isn't rigid enough to take the cuts especially with conventional milling where the cutter will be rubbing at the start of the cut. Which is death to the cutter and the finish. It helps to climb mill, although I don't know if the smaller mills will be up to that?

Andrew

A few more details would help such as vertical height being cut, amount of sideways depth of cut, spindle speed and feed rate for both cutters as well as hss or carbide and number of flutes and also what mill is it.

Edited By JasonB on 04/07/2023 13:03:38

Now you have got the MT3 just be careful to not overtighten the drawbar. I expect the same price offer did not include the R8 model, so there should be more funds available for tooling. Many people keep an er32 collet chuck permanently attached and use it for drills as well as milling cutters. You can buy MT3 socket cleaners which will keep the taper pristine and tooling should be wiped with a clean, but very slightly oily tissue or cloth prior to fitting. There may be recommended drawbar torque figures available, and small torque wrenches are not expensive.

If it is this one then I can't see any mention of brushless which would tend to say it comes with a brushed DC Motor.

The knob on the right side of the head will be the Hi/Low gear change which can actually have advantages over a direct drive brushless as the gears give a bit more mechanical advantage to the motor and it does not have to run as slowly where they can start l lack guts. This is why the brushless option tend to need a more powerful motor.

At low speeds say when using an HSS slitting saw I can stall the SX2.7 with it's 750w brushless motor far easier than the X3 which only has 600W but Hi low range. Gears make a bit more noise but if it's your only mill I would rather have a bit more low down grunt. Different on the CNC when it's doing 5000rpm but I only tend to use small cutters on that.

Edited By JasonB on 23/06/2023 15:56:51

S D ,

Don't have regrets, you've got a good deal.

The only 'But' is that for around £200 more you could have got something similar but with 1.5kw brushless motor and belt drive instead of the 1.1kw motor and plastic/nylon gears in the head. Although you would have to pay £250 or more for a stand and tray. Spare parts could be a bit of an issue in the future but otherwise it's a very good price.

MT3 versus R8 - I wouldn't worry about that now. You've done well.

Hugh

I haven't yet.

I bought MT because at the time MT tooling was more common than R8, and because it allows some tools to be shared between lathe and mill.

In practice most of my milling is done with ER collets so I rarely change between MT tools.

Main problems with MT, I think, are:

1. The need to undo a drawbar means it's not as quick change as later systems (I don't care)
2. Failing to tighten the drawbar means the tapers might spin and be damaged (not a problem for me yet)
3. Over-tightening the drawbar, especially if a cold tool is inserted into a hot spindle, can jamb it in place. The tapers can also stick if left in place for a long time, perhaps due to very slight corrosion or oil gumming up. Removing a badly stuck taper is difficult!
4. Tapping the drawbar sharply with a dead hammer to unstick the taper causes many to assume bearings must be damaged. Actually, although MT has been in wide use for about 150 years, there's very little evidence of this. Nonetheless people believe it. My mill is 7 or 8 years old, bearings are OK.
5. MT relies on a friction grip, which is very strong, but other systems provide positive locking. These allow more power to be put into the cutter, probably more than a hobby lathe can cope with, but accidental breakages of tools and holders become more likely.

Of these only the possibility a seriously stuck taper worries me. So far I've avoided it by not leaving MT tapers screwed tight for long periods - I undo them every six weeks or so and give them a wipe.

I think the main advantage of R8 in amateur hands they don't jamb. Plenty of tooling available for R8 now, so one of my original reasons for choosing MT has gone. Nor is it common for me to swap MT tools between mill and lathe.

For what I do MT is fine, R8 avoids a potential problem but in practice MT vs R8 makes no difference in my workshop. Be aware that not everyone thinks R8 is the best of all possible systems! I'm happy when tools do the job, and don't upgrade them unless there's a specific benefit.

Dave

I'm not sure R8 is due to working on and with "Big Stuff" the actual cross section of a MT3 is no bigger than R8.

The Bridgeport being R8 would really have been the deciding factor and up to a few years ago most hobby mills would have been MT so that really decided it for you. No we see R8 being a lot more common on the smaller machines, whether that is due to the large American market having a lot of R8 ex Bridgeport tooling about who knows

I'm sure if the Bridgeport came with INT taper then Andrew may have gone for that, I would not be averse to a small quick change INT20 for the CNC and if the same tooling could be used on the other mills all the better. I think the late JS was able to spec his Sieg machines with this type of taper.

I suspect it will depend on what you plan to do with the mill.

R8 ( and MT) collets are designed to hold specific diameters of material, so If you only ever use a small number of sizes of cutters then R8 ( self releasing) would be better. If however you will be using lots of smaller cutters, then you might want to consider an ER collet system where the collets hold a range of sizes ( and are cheaper than R8 or MT collets).

If you go the ER route, then once the MT3 shanked ER collet holder is installed, you will only rarely need to get it out, and probably will not really notice the difference.

On my small (MT2) mill I usually hold drills in the ER collets unless I am planning a significant drilling session with multiple sizes.