|michael jones 16||08/10/2019 12:47:46|
|4 forum posts|
Hi . Would welcome advice on this vexing problem please.
I have a WM18 mill which was purchased last October at the Midlands exhibition so is still just about in warranty. I am awaiting a reply from Warco but would like to know if others have experienced anything similar. I have been using the mill until now for simple surface machining and occasional drilling operations which the machine quill was used . All these operations involved milling with the main column locked. I have also machined a few through slots which were started with a suitable drill. All these operations were successful and I have been very pleased with the machine up until the start of last week. When for the first time I attempted to create a enclosed blind slot which by necessity needed to be started by plunge milling into the work piece with a 5/16" slot drill.. ( Both table axis's and quill locked , column unlocked and used to feed .) Horror of horrors .When the cut started the milling head quite visibly moved causing the machine spindle to appear to ir move in a circle around it's true axis.. The hole produced being visibly larger than the cutter by approximately a millimeter! The work piece is now wrecked but I thought it wise to continue to form the intended slot.. The column was then raised and locked to allow a suitable depth of cut and the X axis unlocked and machining commenced . This latter operation progressed with no issues. However overall the slot is somewhat keyhole shaped , no way as intended. Since the cutter was brand new and I was a suspicious of it's end gashing I order other cutters from different sources and repeated the exercise on scrap material. All progressed with similar disaster. Observing that the milling head body was shaking by about a millimeter when applying the plunge into the work , I decided to progressively apply the column locks bit by bit . Eventually the head movement subsided to a acceptable level. However at these settings considerable amount force is needed on the column hand wheel to apply any cut. Surely this cannot be right. By my consideration the machine has had insufficient use to have worn an appreciable amount.
I made a phone call to Warco regarding the gib strip adjustment and proceeded with gib adjustment. On adjustment of the gib so as to limit the head shake to a total of 3 thou of an inch ( where column movement is quite stiff) I find that further up the column this slackens of but at the very top it is impossibly stiff one needs the biceps of 4 African elephant thighs to move it. Mmmm I proceeded then to make some measurements of the dovetails on the column and find alarmingly that there is approaching differences between top and bottom of about 5 thou ! .....not good. Whats more on close examination of the top of the column reveals a serious machining defect, the surface grinding of the right hand dovetail seems not to have reached that far and the initial machining is seen to be very uneven , the ground surfaces seem to be unworn elsewhere.. No wonder I cannot adjust the gibs correctly and very much doubt whether they were in the first place.
What I would like to know is am i asking too much of a low cost machine in expecting it to be able to slot drill a blind enclosed slot and what sort of level of run out at the spindle should I reasonably expect.. Also what should the dovetail angle be it looks non standard to me. From my industrial training days many years ago was a bread and butter job for a vertical mill. Having read of model engineers converting this model of machine to full CNC my mind struggles to see how if their machines were like mine to start with.. Am I doing something wrong , have I overlooked something?
When I purchased this machine it was with the view to follow their footsteps but not now , I feel very dejected.
Any thoughts or advice would be appreciated.
m j j .
16240 forum posts
Obvious question why not use quill fine feed to put on the cut?
Edited By JasonB on 08/10/2019 15:33:19
|Dave Smith 14||08/10/2019 15:52:05|
|78 forum posts|
My WM16 has tight spots on the 'Z' vertical axis, probably due to similar issues to yours. These machines are very much built to a price. The difference in the quill axis position (checked with my DRO's) between the headstock locked and unlocked is about 0.25 mm in X and 0.15 mm in Y. Hence I always lock the headstock and use the quill feed as Jason says. I thought this was normal practise anyway. The few times I have run unlocked you can tell with the vibration. Also check the quill bearing shaft bearings, mine was just out of warrenty when the bearing retainer for the lower bearing worked loose and the shaft started wagging all over the place breaking the cutter.
Lock it all up and try the same cut again. If it is still bad then you need to go back to Warco.
16240 forum posts
You can also help the machine buy drilling say a 6mm blind hole so the slot drill can plunge more easily as there is no slow rotating "dead spot" in the middle or ramp down into the slot rather than plunge.
What make were the cutters you tried? What was the material being cut?
Edited By JasonB on 08/10/2019 17:03:44
|4696 forum posts|
The movement sounds a bit extreme but, like Jason and Dave, it hadn't occurred to me to plunge cut by moving the whole head. I've always assumed the quill was the feed for both drilling and milling. I use the main Z handle only to set the coarse position before locking the headstock and using the quill for accuracy. Just tried plunging with the main Z-feed alone and wasn't impressed. The movement is quite crude and hard to control and feels clumsy in comparison with the quill.
My WM18 doesn't have the gas-strut supplied with later models to make winding up easier by balancing the weight of the headstock. Perhaps because its weight is unsupported my headstock shows little sign of moving, I wonder if the gas-strut models are less rigid because the headstock is supported and has to be locked on those models? Do you have a strut?
I've not had to adjust the gibs on mine yet. If they're like those on my lathes, the adjustment is a bit of an art. On a good day I get it right first time, but I'm not surprised if the traverse is too tight at one end and I have to start again.
Always possible your particular mill is a rough example, but it cut OK on the quill. With luck someone who's converted a WM18 to CNC will comment.
|Dave Halford||08/10/2019 18:02:25|
|459 forum posts|
Plunge milling is very aggressive it'll find any lash in the Z.
Is the column moving and adding to the problem?
|Sam Longley 1||08/10/2019 18:14:14|
|721 forum posts|
My WM16 shakes all over the place even when drilling a simple hole. It vibrates so much that I have elastic bands on the control box to try & stop it shaking itself to bits. The head flexes from side to side visibly.
The unit can be clamped as tight as possible & it just flexes.The whole column seems to bend. Not much use as a mill, unless machining plastics etc.
Mostly I use it as a pillar drill.
Very disappointed with it.
2449 forum posts
Maybe a silly question; is the locking nut under the head working loose?
'Hence I always lock the headstock and use the quill feed'
I do the same then do any depth adjustment with the fine feed.
|old mart||08/10/2019 18:52:00|
|538 forum posts|
Jason B's suggestion is best, leave less material for the slot drill to plunge into. A solid carbide four flute end cutting mill will plunge much better than a two flute slot drill, which is preferred for the actual slotting.
|Ian P||08/10/2019 21:37:30|
2171 forum posts
A starter hole is the best way to go but if I'm in a hurry or cannot be bothered to change the cutter from say a standard endmill or a non centre cutting slot drill, I just move the job from side to side a short distance whilst feeding the cutter down with the quill. I rarely use the cutter the same diameter as the finished slot so then clean up the slot to width once the bulk of material is removed.
Plunging any flat bottomed-ish cutter into a flat surface is always going to be challenging unless the machine is ultra rigid.
315 forum posts
Whenever I have had violent shaking plunging on a 2 flute cutter it has always been cutting one of those weird Reuleaux triangles rather than a round hole. I have no idea why or how to prevent it, we have already plumbed the full depth of my knowlege with this simple observation
3695 forum posts
There's probably no getting around the sloppiness of cheap and cheerful, or old and worn, machine tools.
I'd try as suggested, drilling the hole to start with by a conventional 120-degree-point drill bit, a bit undersized and then take the final skim plunge cut with a slot drill and proceed on milling the slot.. Using the quill feed to set depth etc.
Next time it gets to dancing around like that, take a look at and put a finger on the join line between the column and the base. Sometimes if those two mating surfaces are not very accurately machined and matched, the column can be a bit unstable in operation. I've seen one that looked like it was machined with an angle grinder wielded by Blind Freddy at 3.58pm Friday afternoon. .
|1182 forum posts|
Did you use ground bars to measure over to obtain the dovetail widths ?
Design concept is good with dovetailed column with tapered gib but if you have .005" difference on width top to bottom then the gib adjustment will only be correct at the point it is adjusted at.
Like others have said I also would have put the cut on with fine feed with the column locked, especially on that machine as the head down handle is placed at the very top of the machine.
Finding ways around any machine defect doesn't help very much with any warranty claim but does highlight the fact that when receiving a new machine it should be checked thoroughly to find any such problems that can be reported immediately to the supplier.
"Buying a milling machine from Warco.
Above para from Warco's site, did you get an accuracy report ?
I believe if you contact the supplier they will be helpful.
|michael jones 16||09/10/2019 11:49:51|
|4 forum posts|
Many thanks for taking the trouble to assist.
I think the last post has almost hit the nail on the head. Except in my instance Blind Freddy was recovering from a Friday lunchtime binge and day dreaming about a weekend binge with his mates! It appears to me that these tapered gib thingies can't hold the head securely on their own with out some support from the locking screws. My guess at the moment is that since the gib thrust is applied from the ends of the gib strip a degree of buckling of the gib may be allowed to take place that allows the head to move about on the dovetails. Looks like Blind Freddy was given the freedom to fashion the dovetails on the column and possibly the milling head as well. My impressions at the moment is that the angled part of the dovetail looks somewhat convex rather than flat , even where the possibility of wear if any is unlikely to have taken place. But I really need to investigate this aspect further.
I had considered using the quill to apply feed in the first instance but I am re aqauintting myself with the art of milling and also I am exploring the envelope of performance / abilities of this machine. ( My only exposure to mechanical engineering was a year spent in basic training at the onset of my career some 50 + years ago. You couldn't call basic these days as we covered every aspect from foundry work through to metal spinning , sadly though we didn't get time to do any gear cutting or hand scraping. So I'm a bit rusty.) Thinking that the quill would add additional length to the cutter and there by add another variable to the exercise.. it's certainly discovered a major limitation. The same goes for first drilling under sized holes/ slot to start in the first instance.
To answer a few questions , the material was BMS. As for the cutters , the first two I used were from one of those boxed sets I think I possibly bought from a reputable trade stand at an exhibition but one of the others was from a cutter purchase from Arceurotrade and two would you believe were industrial throw outs long since past their supposed life with tip cutting edges freehand sharpened by myself on the bench grinder! The last were done in a fit of frustration and an element of try and see approach. Surprising they cut very very freely compared with the purchased items . I expected head shake and hence the first plunge to form the slot to be far worse ...... not the case there was no difference. So it's down to the mill.
I guess my main problem is having spirits raised by my satisfaction with the machine up until this issue and of course be encouraged by the fact that some gifted people have been sucesful in converting this type of machine to CNC. ( Which was one of my main aims.) Now has painfully been dashed on the rocks.
Once again thank you all for your kind assistance. I think i'll go off and see if I can find a comprise adjustment for the gib. I might also consider fitting some setting screws to the head to limit limit the freedom of the gib when the standard locking is loosened.
Oh by the way does anyone know what the angle of the dovetail should be?
Regards all . mjj
|michael jones 16||09/10/2019 12:05:27|
|4 forum posts|
To reply to the latest post. Hind sight is a wonderful.thing . I probably just too happy with the performance in the first instance to try every aspect. The rods used were fully ground ( 0.4997" measured at various points on the circumference and along the the bars ( approx 6^ long so they take an average ).
I have emailed Warco but have not yet had a reply.......I have tried phoning but the tech' phones are just too busy.
|Andrew Johnston||09/10/2019 12:10:12|
4851 forum posts
The basic problem probably is the mill. But using poor cutters (not the one from Arc) certainly won't help matters. Small machine tools need all the help they can get, including quality cutters properly ground.
If the gibs are proper tapered ones, they don't have locking screws, just adjustment screws at each end. Presumably the gibs are parallelograms rather than proper tapered gibs?
16240 forum posts
I can't speak for Warco but ARC certainly advise putting on a cut with the quill fine feed not the head height handle, why else would the built in digital readout be fitted to measure the fine feed, the head only gives a coarse reading.
Also not good from a safety point of view to be reaching up over a rotating cutter to make adjustments.
Was it one of ARC's premium cutters or the basic Gold Tin coated ones? if the gold then I'm not too keen on those.
I just popped a 6mm 2-flute standard length premium HSS cutter from ARC into the SX2.7 as that is the nearest I have to your cutter, did two plunge cuts one with fine feed and the other with head feed and no real difference in the holes produced, head feed did feel a bit more like things were moving about but that could just as easily have been the lack of control of the feed. I then cut between and beyond the two 2mm deep plunged cuts and in both cases no sign of the plunge cuts being oversize. Red marks are where I plunged
Edited By JasonB on 09/10/2019 12:30:39
Edited By JasonB on 09/10/2019 12:31:30
|old mart||09/10/2019 22:34:59|
|538 forum posts|
I remember plunging a 1/4" slot drill about 1/4" deep and getting a hole 0.015" oversize. Changing the cutter resulted in a hole only 0.001" oversize, yet there didn't seem to be much difference in the sharpness.
The trouble with plunging two flute slot drills is that viewed end on they are asymmetric, so they drill like a badly sharpened twist drill. For cutting the actual slot, two and three fluted mills are much preferable to four fluted as the 90 degree separation of the cutting in the four flute interferes with the cutting.
Recently, I wanted to cut a quick flattish bottomed hole in a piece of 23mm square aluminium. The hole was 3/4" diameter, and 1/2" deep. The aluminium went in the lathe four jaw and a new Osborn slot drill went in the tailstock chuck. The tailstock was shaking at least 1/16" when I made the hole.
Edited By old mart on 09/10/2019 22:43:26
1241 forum posts
I have a WM16 lookalike and it doesn't do any of the things you describe .... unless I try to take a ridiculously oversized cut (such as unintentionally running the cutter into something under the x-power feed). I don't believe your experience is typical of these machines and it would be well worth investigating the cause.
|4696 forum posts|
I wondered about Sam's comment too. I have a WM18 which doesn't behave like that unless mistreated, but I also know that Chinese machines are a bit rough, typically poor finish and assembly, and there are also a few delivered with actual defects. Bad castings, and miscut dovetails, etc. sometimes reach the customer even from reputable suppliers. Possibly Sam has a dud machine or one needing serious fettling.
Faults apart there are plenty of other reasons why a WM16 might behave badly. First, the design of these small mills is seriously compromised to reduce cost and weight. For example the column includes a single bolt to allow angled cuts, and - in addition to making tramming awkward - this crude hinge is a structural weakness. To a physicist the column is nothing but a crowbar with g a heavy weight, the motor, at the far end. The whole machine is top-heavy, making vibration more likely. And the column's strength is reduced by dovetails and a lead-screw channel, making it likely to bend. Bottom line, these machines aren't designed for heavy milling.
Second, because the design is a compromise, it's important to avoid anything that will over-stress the machine:
Andrew Johnston's recent article about his Bridgeport Mill in MEW286 is recommended. Compared with the WM16 (113kg) the Bridgeport is a far bigger machine (2000lbs/ 900kg) and much more attention is paid to stiffening up by the Bridgeport's design - look at Andrew's photographs. However, note Andrew's comment in the 'Using the Mill' section, 'The keyword when describing the Bridgeport is versatility, although this does come at the expense of rigidity'. I don't believe Andrew is suggesting his Bridgeport is a wobbly heap of junk, rather he's recognising that it too is a compromise and - like all machines - has limitations that can be addressed by skill. We live in the real-world.
I see hobby milling machines as being for precision filing and drilling in small workshops. Whilst they save time I don't think they're intended to remove metal at high-speed.
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