Stuart Twin Victoria (Princess Royal) Mill Engine

[Dr_GMJNParticipant @dr_gmjn]

So now the weather is much better, I’ve re-started this one. In the end I decided to re-make the forks, mainly to get into using the equipment again.

I’ve immediately run into the the same old issue with milling – poor surface finish. I set the 20 mm square steel stock in the vice and milled the top and sides, then the slot as per last time. The probelm is I’ve ended up with chatter on the short sides, which will still be visible once the ends are rounded off.

I’m using a new slot drill and then tried an end mill. I’m setting the x and y dimensions and incrementing down about 1 mm at a time to a total depth of 15 mm. The first one turned out pretty well. But the next two are hopeless. I thought the issue was taking final sized cuts all the way down, so I tried incrementing down, then across in 0.01 mm steps for the final full-flank cuts, to no avail. Exacty the same result. Interestingly, it’s worse on the short edges, not too bad on the wide sides. Unfortunately this is no use to me since those good faces will be turned down to form bosses in the lathe. The slot was milled last, after the chatter appeared, so it’s not like the reduction in workpiece stiffness was to blame.

I’ve had this kind of issue since day one when machining steel, and have asked about it before several times. I’ve tried all kinds of adjustments, locking axes, feeds, speeds, tools, but it always seems to end up like this at some point (or worse). I can’t put up with it much more, it’s just causing me huge frustration and eating my limited free time.

Thanks!

[JasonBModerator @jasonb]

Consider doing it with the parts laid flat as you have them in the photo. use a vice stop so you can maintain position as you change their position in the lathe.

Would be worth trying similar cuts as you did but with the orientation 90deg and see if you get chatter on the long sides which would indicate a problem in one axis.

Detail of feeds and speeds would help. If doing them vertically as you have then I would be coming down in steps of 5mm – 6mm rather than 1mm and stepping over say 1mm, finish full depth at 0.1 to 0.2

Similar item done horizontally in a collet block but vice would do

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason.

Are you suggesting doing them in the lathe somehow? You wrote “as you change position in the lathe”?

Not sure how I’d get the dimensions correct without a lot of measuring out of the vice then adjusting the cut depths?

I looked back a couple of pages and as it happens  last time I machined them, they were at 90 degrees (rotated vertically) to the orientation I used this time, and it was still the y-axis faces that gave the bad surface finish.

I can’t tighten the y-axis any further because it’s already too stiff (like the x-axis to be honest).

 

[Dr_GMJNParticipant @dr_gmjn]

So to be clear, this was the orientation last time. It actually grabbed and took a chunk out of my vice which really pi**ed me off:

Short side:

And this was the orientation this time (Long side had the error, although this is actually the one side visible that wasn’t too bad):

[JasonBModerator @jasonb]

Sorry Typo, should have said “position in the vice.”

If it is the Y axis that seems to be the problem then you could do two sides in X and then turn the part 90deg in the vice and do the other two faces then it will all be cut in x

Lastly with that type of vice make sure you don’t have the jaw at the end of it’s tightening movement. As the screw gets further in the tightening force becomes more downwards than horizontal and it may be the work is not stable in the vice. Wind the screw out and use the next notch closer to the fixed jaw.

[Dr_GMJNParticipant @dr_gmjn]

OK I’ll try x-axis only, although it removes a lot of functionality and adds a lot of hassle if I’m having to do that all the time.

The SX2P is a strange design, with the backlash on the head rack and the odd table offset under the spindle. I could get rid of it for a better machine of similar size, I would. Are there any decent alternatives? I’d much rather have something of ML7 quality/age, and don’t mind looking around for one.

Thanks.

[Ian HewsonParticipant @ianhewson99641]

Last photo, the end mill looks very long and thin.

Are climb milling one face but not the other?

Regarding mills, my SX2p works fine for that size of work.

Ian

[Dr_GMJNParticipant @dr_gmjn]

Ian,

That’s a drill not an end mill.

My SX2P has never been happy milling steel right from day 1. I’ve tried stripping and re-building the slides, adjusting gibs, tramming, different tool sizes, speeds and feeds, all to no avail.

Conventional milling on all faces.

Thanks.

 

[Martin ConnellyParticipant @martinconnelly55370]

What you are calling chatter looks like dwell machining to me. This happens when a flexible set up (they are all flexible to some extent) is allowed to dwell too long in the middle of a cut so the cutter has time to do spring cuts in one location only. The result looks just like what you have there. This is problem with manually feeding and the slower you try to feed the easier it is to have these problems.

Martin C

[Dr_GMJNParticipant @dr_gmjn]

Thanks Martin. Could be that. I try to be as smooth as possible using the wheels. I also go back and forth after the first cut. *final cut*

Strange how I use the same technique and some faces are fine, others are terrible.

[JasonBModerator @jasonb]

I’ll leave it to the “old Iron” fans to suggest some machines but in the meantime I had a go with the SIEG SX2.7

Initially cut as I said yesterday with 5mm vertical x 1mm horz DOC using one of ARC’s 3-flute HSS cutters at 1500rpm, then upped it to 10mm vert and finally 15mm vert all with 1mm stepover. Finish cuts 15mm vert x 0.1mm hor.

The slot I did with another of ARC’s 3-flute HSS but this time 6mm dia at 2000rpm. Roughed out at full 6mm width x 1.5mm deep and then full 10.3mm deep x 0.2mm stepover to take the slot out to width. Video of the slot being roughed did not come out so have linked a second video with some similar slot cutting action.

Not too bad considering I was feeding single handed and as you can see reasonable chips and a reasonable feed rate. Neither cutter was new

[Dr_GMJNParticipant @dr_gmjn]

I can’t see any images or video.

[JasonBModerator @jasonb]

Anyone else not able to see them. I can on PC and phone logged in or not?

try here

and here

[Dr_GMJNParticipant @dr_gmjn]

I can see two videos now. For some reason I got logged out.

Thanks.

[Dr_GMJNParticipant @dr_gmjn]

OK thanks Jason. I guess I’ll get some more steel and cutters and try again.

There’s obviously something wrong with the y-axis (or the head when loaded laterally) of my machine, so I’ll have to limit my cuts and orient the workpiece such that I’ll be turning bosses on those faces.

[Dr_GMJNParticipant @dr_gmjn]

I found I’d got one bit of steel left, so had another go using smaller cuts, and using two 0.01mm finishing cuts to get to size.

I also turned the work so that the previously problematic y-axis faces would be the ones that would be subsequently turned down for the bosses.

This time, the y-axis faces were fine, and one of the x-axis faces:

But now the opposite face – using exactly the same cuts and conventional milling, looked like this:

These were the faces on the x-axis which were fine last time.

Much as I hate to compromise, I then face milled the gouges away, and have obviously ended up with slightly undersized parts (about 0.005”).

This is the fifth sixth attempt at these, and I think if I have to do them again due to some knock-on effect of this screw up, I’ll pack the model up and call it a day. It’s just not fun any more.

I need a much better quality milling machine, because this thing is driving me crazy – I seem to spend as much time fighting a losing battle either trying to adjust it, or correcting errors caused by it.

 

[Ramon WilsonParticipant @ramonwilson3]

Doc – Just caught up with this. Good to see you doing something but not to hear your frustration.

Personally were I to be making these parts I would not be using the side of the cutter – certainly looks like cutter pull in to me. Bar stock material is not always easy to machine and can be a bit claggy’ which doesn’t help. I know the ‘easy’ way of squaring stock by going around the sides is appealing but you need sturdy kit – millways, spindle and cutter to get a good result. I think with your set up you would be much better end milling the faces than side milling even if you have to take longer. If the gouges you show on your second side are from cutting on the end then something is definitely loose as the cutter is pulling in or the work pulling up

Also you might (personally I would) be better off using En1a round material held in the vise and four flats milled on then using it as ‘square’ stock – you do not have to mill it to a full square – just four flats adequate enough to grip in the vise. Once ‘sided’ hang it out the vice to do one end then reverse to do another at the other.

Whatever, don’t despair on the mill – just do your best to work around it’s issues – believe me I worked with some pretty sorry kit in my day, some really not fit for purpose but there’s always a way around things even if the time goes up

 

[DiogenesParticipant @diogenes]

Somewhere in one of your posts above you mention something like “gibs are tight – almost too tight”..

If they are ‘sticky’ or ‘notchy’, when a series of small cuts are required, a situation can occur where one or two handwheel movements will only serve to load up the screw / nut against the binding, only for the next to overcome the ‘stiction’ and the table to spring free resulting in a much deeper cut than expected.

[JasonBModerator @jasonb]

Good to know Ramon would have done it laid flat like I also suggested. My photos also show round freecutting stock.

That last photo certainly looks like the cutter is deflecting into the work again a problem, the last bit where it has not cut is is where the middle of the cutter has reached the end of the cut so there is less force pulling it in.

As for material if you don’t have more then there looks to be enough on the opposite ends to use, Infact it would have been a lot less wasteful to cut one piece and work both ends rather than cut two pieces and have two lumps to go in the offcuts box.

0.01 passes are really too small and will tend to rub, try 0.1mm

 

[Martin ConnellyParticipant @martinconnelly55370]

Overtightened gibs could be the reason for the dwell issues and would explain what I am seeing in the earlier photos.

I know a lot of people advise against this but I would consider climb cuts for the last few 0.1mm passes on this material. If you have snug gibs then the forces should be low enough to avoid dragging the work and bed along. This would avoid the situation you seem to have at the moment where the table is moving in a stop go manner and where it is stopping it is springing into the workpiece due to the conventional milling forces. There are a number of reasons why CNC users use climb milling for a lot of what they do, it is not just because they can. Try an experiment on some scrap before using it on something with a lot of work put into it.

https://www.harveyperformance.com/in-the-loupe/conventional-vs-climb-milling/

Martin C

[JasonBModerator @jasonb]

regarding the marks in the last photo, this image may go some way to illustration how the cutter has been pulled into the material.

On the left is a pass taken with a 4 flute cutter that was past it’s best. The green arrow indicates where it stopped being pulled sideways as the middle of the cutter exited the cut just leaving the last bit cut as it should be. Cutter moving in the direction of the red arrow and being deflected in the opposite direction to rotation shown in blue. This is the same sort of thing you get if you use a 4 flute cutter instead of a 2 flute to cut a slot.

Pass on right exactly the same cutter and setup but after cutter had had it’s end sharpened.

What your image shows is a series of such deflections as you have stepped down the job. Check it has not got blunt, particularly the  corners.

Same cut from above that shows the deflection along most of the length and also the much more pronounced rings left on the bottom of the cut where the cutter is riding on the surface compared to the right where it is actually cutting.

[Dr_GMJNParticipant @dr_gmjn]

Thanks all.

I might try loosening the gibs a bit, although I’m sure this will result in the axes rocking slightly. I expect this will make things worse, but it’s worth a try. Of course non of this will solve the head pulling down issue.

Noted about using end milling to machine the flanks, but after incrementing the flank cuts with a few more passes, the surface finish seemed fine on three out of the four sides  (as it was previously really). I don’t get why, if the cutter was blunt, it could have produced a good finish on most of the sides on multiple workpieces. It’s not as if all the good sides were done, then the cutter got worn and started to get dragged in to the surface for the final surfaces on each workpiece.

Reason for using a lot of stock was to have enough to grip in the vice. I then drilled the central hole for tapping at 0,0, right between the forks. I might have enough for a couple more goes at face milling the geometry on them, but I guess it would involve a lot of facing, measuring and re-setting into the vice to get the right depths and widths.

I was looking at other milling machines and found a Tom Senior. Any experience of these? They look fairly compact, although are free-standing rather than table mounted (not an issue).

[JasonB]

On JasonB Said:

Anyone else not able to see them. I can on PC and phone logged in or not

Apologies for the much delayed response:

Can’t see either on the iPad … just white-space.

This is, I believe, the Bug that I have already reported:

i.e. They are there, but hiding under a layer of opaque white.

MichaelG.

[Dr_GMJNParticipant @dr_gmjn]

I trudged on with the forks and accepted that they will never be perfect. I turned the bosses and collar in the lathe. No point posting pictures becasue I’m just repeating what I did before.

Today I rounded the ends in the R/T (last time I used filing buttons, but wanted to get back into the swing of things, so did it a more elaborate way):

Here they are compared with the too narrow versions I’d made previously:

So now I’m pretty much back to where I was almost a year ago – about to pin the crosshead shaft to the forks. I’d already bought the pins and taper reamer:

I need to figure out how to hold everything in the mill for drilling the hole for the reamer, and hope that the drill(s) don”t break when the hit the fork/shaft interface. Any advice on setup & precedure for this whole thing much appreciated! I think Jason you mentioned drilling two diameters of hole before using the reamer?

Thanks!

[JasonBModerator @jasonb]

For the small pins like that I do tend to drill stepped holes. Measure a little way up from the small end of the pin and again about half the fork thickness from that and size your drilled holes to suit. Take it very easy with the reamer as they are slender but there will be a lot of flute engagement. Remove often to clear the swarf always making sure to turn clockwise, use cutting fluid

A small piece of aluminium packing against the pin will allow it to be held in the vice without the pin moving

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