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Post by simplyloco on Jul 28, 2020 19:38:44 GMT
Even I run a 3/32" cutter at 4250 (my maximum). I think its the feed rate that I'd be way down on, more like 25mm/minute. I was not taught linear feed rates: feed per tooth was the maxim based on the cutter size, then rpm to suit the material. That way I knew the cutter wouldn't be over stressed. Usually...  John |
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Post by Roger on Jul 28, 2020 21:07:50 GMT
Even I run a 3/32" cutter at 4250 (my maximum). I think its the feed rate that I'd be way down on, more like 25mm/minute. I rarely go more than 50mm/min on Steel with any size cutter, more usually 30mm/min. It all depends on whether you're wanting to rip through the material like they do in industry, with massively rigid machines and flood coolant. You can certainly do it like that on our machines, but the price is horrendous noise because our machines are flimsy, and creating a lot of heat in the process. Personally, I don't see the point. Taking things gently and smoothly gets the job done without fuss and you can walk away with confidence that it's not going to go pear shaped. Cutters last longer and jobs don't move because the forces are lower. Sure, it takes a bit longer, but who cares? |
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Post by David on Jul 28, 2020 22:36:01 GMT
Taking things gently and smoothly gets the job done without fuss and you can walk away with confidence that it's not going to go pear shaped. Until the cutter pulls out of the collet and rips through your table. I deliberately set the parameters for this cut slow in an attempt to avoid dramas. I used the roughing cutter in the probably mistaken belief the cutting forces would be less with it. That was a guess. Next job is to put the fire door and knee guards on, and then make a warming tray. |
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jasonb
Elder Statesman
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Post by jasonb on Jul 29, 2020 6:33:02 GMT
The problem is going too slow can have the opposite effect and wear the cutter due to rubbing.
Assuming that roughing cutter was 4-flute and carbide if you were running at say 4000rpm and feeding at 30mm/min that is a chip load of 0.0018mm which is less than 1/10th of a thou which is not a lot. ( what do those using chip load calculate?) It is more what I would be hand feeding a HSS tool at on my manual mill for deeper cuts where the speed would be down to 1500rpm or so on a 1mm depth and full width of 6mm cutter I'd be more like 75mm/min at those revs with HSS.
I also take into account the type of cut and amount being removed rather than just using a blanket feed rate, for example I tend to do 3D finish contour cuts at 500mm/min but as they only use a very small stepover of 0.25-0.33mm the load is very low and if I did them at 50mm/min the one I did the other day would have taken over a day to run! But on something like adaptive clearing with a 3-flute carbide on steel I'd be going 300-350mm/min with a 6mm dia cutter and something in the region of 6mm step down and 1mm stepover and spindle speed of 4500.
I understand that those with slower top speed and noise issues will maybe have to moderate their cutting but there are other ways that are still not that noisy or detrimental to machine or cutter.
If you are worried about the tool pulling out on cuts like that then use thicker packing below so that if the tool came right out it would not reach the table, couple of layers of MDF for example. Also if that was hot rolled plate you were cutting think about acid dipping to remove the scale first as it will blunt the cutters faster particularly when slotting.
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Post by Roger on Jul 29, 2020 11:03:02 GMT
The problem is going too slow can have the opposite effect and wear the cutter due to rubbing. . It will only rub if you don't use an appropriate RPM so that it fails to keep cutting. You can go as slowly as you like. The problem with a lot of light hobby machines is that you can't slow the spindle down enough while still maintaining sufficient torque to do this. My mill can go down to say 30RPM and have enough torque to use a 65mm cutter at that speed. |
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jasonb
Elder Statesman
Posts: 1,239
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Post by jasonb on Jul 29, 2020 12:29:48 GMT
Yes that's true and without knowing what speed David was running at hard to really comment but I assumed with a carbide 6mm cutter he would be running at the recomended surface speed so something in the region of 75-100m/min. As his mill is a similar weight to mine he should be able to take similar cuts.
I say it a lot on ME but the smaller machines are better off running a highish spindle speed be that a lathe or mill and take a light depths of cut as if you are running at double the spindle speed and half the DOC it takes no longer than half the spindle speed and the full DOC which keeps the motors in their power band rather than loose torque running them slowly. The other Tormach user that I know is also an advocate of smaller dia tools at a good speed and feed and very much likes to do the calculations to get the correct chip loads etc , infact he only commented last week that I was feeding a bit slow on a video I posted where the feed was 500mm/min in steel. Makers speeds for that cutter and type of cut would have been 2000mm/min feed but I don't run at those as it's a light machine and I also need to drop the speed as well from suggested 8000rpm down to my 5000rpm max, I always try to run at suggested spindle speed.
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Post by Roger on Jul 29, 2020 14:27:50 GMT
Yes that's true and without knowing what speed David was running at hard to really comment but I assumed with a carbide 6mm cutter he would be running at the recomended surface speed so something in the region of 75-100m/min. As his mill is a similar weight to mine he should be able to take similar cuts. I say it a lot on ME but the smaller machines are better off running a highish spindle speed be that a lathe or mill and take a light depths of cut as if you are running at double the spindle speed and half the DOC it takes no longer than half the spindle speed and the full DOC which keeps the motors in their power band rather than loose torque running them slowly. The other Tormach user that I know is also an advocate of smaller dia tools at a good speed and feed and very much likes to do the calculations to get the correct chip loads etc , infact he only commented last week that I was feeding a bit slow on a video I posted where the feed was 500mm/min in steel. Makers speeds for that cutter and type of cut would have been 2000mm/min feed but I don't run at those as it's a light machine and I also need to drop the speed as well from suggested 8000rpm down to my 5000rpm max, I always try to run at suggested spindle speed. It's certainly true that lighter spindles can benefit from higher spindle speeds and higher RPM than I use on mine. My high speed spindle attachment goes to 24000RPM and is at the other extreme to my normal spindle. A 6mm cutter is too big for that really, the shaft simply isn't rigid enough to resist chattering when even a modest depth of cut is used, and it runs out of torque. It's handy for routing with 0.5mm cutters though. I'm probably going to make an adaptor for another belt driven spindle that I've got which is much more rigid, and that's good for 24000RPM too should the need arise. I don't take any notice of recommended spindle speeds. In my opinion they are only appropriate for rigid industrial machines. I think I'm better off using my experience, listening to what the machine is telling me, rather than trying to enforce numbers that aren't optimal for my machine. |
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Post by jon38r80 on Jul 29, 2020 19:27:15 GMT
" listening to what the machine is telling me, rather than trying to enforce numbers "
+1
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Post by David on Jul 29, 2020 22:58:48 GMT
Jason, do you use coolant when cutting?
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jasonb
Elder Statesman
Posts: 1,239
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Post by jasonb on Jul 30, 2020 6:14:38 GMT
No, just a little paraffin when working aluminium, I did start by brushing on a little soluable oil when cutting steel but don't bother now as it tends to collect the chips and you end up recutting them which won't do the tool or finish much good. Keep meaning to get round to rigging up the air with a fog buster type sysyem for the ali but not got round to it yet as I don't cut a lot of ali.
If my machine had flood coolant then I would run it but more to clear chips than as a means of controlling temperature, I'm still not feeding at commercial rathes so not generating much in the way of heat.
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jasonb
Elder Statesman
Posts: 1,239
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Post by jasonb on Jul 30, 2020 6:52:42 GMT
Just looked back at the CAM for this part which is a similar operation to yours and was one of the first items I did so a bit slower as I was still finding what the machine could do but five times faster feed than you used.
6mm 3-flute carbide cutter at 3000rpm and feed of 150mm/min. 1mm deep per pass which is what you see in the first part of the video and then the full depth finishing pass of 0.5mm ae. Makers suggest 4100rpm and 490mm/min feed. As always the editing and uploading adds some high frequency noise not helped by camera being 3" from head of machine, its not bad close up.
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Post by David on Aug 4, 2020 12:15:03 GMT
It's not much but it's still progress. I put the bits on the new dummy backhead and made the warming tray.  |
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Post by David on Aug 15, 2020 23:49:17 GMT
Despite all the faffing around with a CAD model I decided to try a dome casting after all. It's getting there. The trick will be knowing when to stop trying to thin the flare (probably now), and getting it off the mandrel. It's stuck on with strong retaining compound and when I had to take it off last time because I forgot to fit the bottom diameter to the boiler I had to whack it out with a drift after pouring a lot of heat into it while it was resting on it's (then) 5mm thick flanges. If I do that now they'll just break. I'll put some MDF pads under it and see how it goes. "You weren't supposed to use the strong stuff!" was the helpful comment I got a couple of days ago... The remnants from the last dome on that mandrel looked green so I assumed strong was the way to go. I have to open the bore out at the base too because there's not enough adjustment space around the inner dome. The current diameter was determined by the mandrel I had. I could use a carbide burr but I'm worried I'll slip and damage the flare. I couldn't get the raw casting to sit nicely in either my 3 or 4 jaw chucks and had to use excessive force on the jaws in the 3 jaw to do the initial bore. Maybe if I put copper wrapper on the chuck jaws and a drawbar through the spindle it will be held well enough to use a boring bar.   |
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Post by Jim on Aug 16, 2020 4:06:31 GMT
Looking good David.
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Post by Roger on Aug 16, 2020 6:57:41 GMT
Hi David,
When you say 'retaining compound', do you mean Loctite of some kind?
If you submerge the whole thing in acetone, in sure you'll get it off. Acetone destroys most adhesives if you leave it long enough.
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Post by Deleted on Aug 16, 2020 10:06:44 GMT
Hi David, When you say 'retaining compound', do you mean Loctite of some kind? If you submerge the whole thing in acetone, in sure you'll get it off. Acetone destroys most adhesives if you leave it long enough. Talking of Acetone, I can share a little story from my film days. A very good friend of mine when working on 'Goldeneye' treated himself to the same Omega watch as Bond wore in the film. It had an anodised finish, Greg being 'Greg' was a bit of a messy worker, his bench was something else in the 'mess' catergory. He was known for ruining good clothes when working with all those nasty chemical/materials which was the norm for us all. Anyway, he was casting some parts in resin and of course, he was wearing his watch. He got the face covered in resin and filler and not wanting to risk rubbing it off his very expensive watch he decided to dip the watch into a pot of Acetone for a short while. Well, that certainly got all the crap off, trouble was it also removed the anodised finish. All was not lost though, he complained to the manufactures who duly replaced the watch under warranty, he didn't mention the Acetone...  Putting aside his carelessness of nice things, he once took my Porsche for a test drive and duly got the leather seats covered in filler, he was and still is perhaps the best model maker from any period out there, a true craftsman. Pete |
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Post by David on Aug 30, 2020 8:35:04 GMT
Got the dome off the mandrel. I heated the life out of it, let it cool down, rested the flanges on some wood to try and avoid breaking them, and got nowhere. It moved perhaps 2mm and I was hitting it really hard with a drift through the hole in the top. I decided that was not the way forward so suspended it in the vise jaws and heated the dome. The mandrel dropped out the bottom pretty quickly as it is quite heavy. It's just sitting there, still need more fitting and the internal bore opened out to give more freedom.  |
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Post by David on Sept 9, 2020 7:06:41 GMT
The dummy backhead and plumbing are the current jobs. My first attempt at using JBWeld for the fire door ring was no a success and I was able to push it out with my fingers. The epoxy had stuck quite well to the ring but not at all to the backhead. Attempt #2 was soft solder. I thought the wrapper had gone so well I'd give it a go. It didn't end well - I couldn't get the solder to flow nicely or the ring to sit flat, and the backhead started to distort despite the fact I was using the smallest flame I could get out of my canister torch. I guess the flange at the edge was what allowed me to get away with soldering the wrapper on without distortion. Attempt #3 was back to JBWeld but with the backhead face up on the bench and a heavy offcut of cast iron as a weight over the ring. This seems to have stuck ok. I have not cleaned the excess off yet. The fact the dummy backhead sits proud of the gauge glass and blower bushes is a big nuisance and I've had to open out the holes and make long nuts with the threads bored out at one end to get things to fit. I assume all the bushes were meant to be flush with the door ring bush so the dummy backhead could sit against all of them. In my case it didn't work out that way and there's about 3mm of air behind the holes for everything except the door ring. No great hassles with the pipes yet aside from the fact my boiler is too wide so the LH injector steam pipe is nipped up between the reversing screw bracket and the backhead. I'll take a little off the bracket and see if that gives enough space. A little pipe bender from e-bay like is used for brake lines has done good work on a lot of the bends with others done carefully by hand around a 1/2" steel bar. The injectors are right over the brake cross-shaft which is annoying. The LH one is ok because the shaft ends just inboard of it but the RH one is right over it and I have to have the injector on a bit of an angle to get the water feed inside the handbrake lever/arm and will have to modify the overflow pipe to have a sharpish angle in it. I have not decided how high the pressure gauge is going yet. I'll wait until I have the roof so I can see if having it a bit lower than Barry does makes a difference. If not I'll put it in the same place. I have bent up a pipe for the blower but not put the unions on yet. I'm not convinced by the 90deg globe valve I bought - it's not like a normal blower valve where you can use a nut to get the alignment right. I think I asked for the wrong thing.    |
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Post by David on Oct 13, 2020 7:00:59 GMT
A month has gone by and not a great deal done. I'd blame work and uni, and they have been a bit busy, but it's not much of an excuse! But a bunch of small but necessary jobs have been done. The cab has moved on a bit. I've trimmed the reversing screw bracket so it's not squashing the left injector steam pipe. Then moving the screw as far to the left as I could on the bracket meant making the opening in the cab front wider but it all fits and works now. The handbrake only just misses the dummy backhead and I had to move the injector steam valve up and back a bit to clear it, but it could be used in a pinch now. I might make the vertical part of the handbrake handle a bit shorter. It could do with shorting horizontally too, but it wouldn't look right. I'm considering a washer under the steam turret nut to clamp the dummy backhead down - it just rattles around at present.  Then the pipes that go from the real clacks to the dummies. These look simple but were anything but! They were done a few times each and are very kinked and wonky. And looking at the photo of the LHS I see the pipe isn't straight. But I've resoldered that union on a number of times now and I don't think I can be bothered. Maybe when it's painted black it won't be so noticeable.   A couple of little clips to hold those pipes to the boiler. That all went well enough until I tried to trim one in the bandsaw because I was too lazy to put a new blade in the piercing saw! The saw got a new blade anyway and did the job after this. It was easy to fix, just press it exactly as was done the first time, it was still soft.  |
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mbrown
Elder Statesman
Posts: 1,790
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Post by mbrown on Oct 13, 2020 7:17:09 GMT
It's coming on well!
You should be able to tidy up that left hand pipe without moving the position of the unions. It looks as if the front bend could be tighter (matching the RGS) which would bring the front end of the pipe a little higher, and then adjusting the bend at the rear if necessary would level it all up while leaving the union where it is now.
In my view, it is well worth getting pipework level as it can gave a disproportionate visual effect overall, sometimes making other parts that are correct look skew-whiff.
That cab interior looks very prototypical.
Malcolm
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