|andrew lyner||19/04/2020 11:51:51|
|218 forum posts|
I have been trying to grind a new HSS fly cutting tool and I am coming on in leaps and bounds. The fly cutter seems to be the most understandable cutting tool because you can lean down and see all the angles at work - just like in the not always helpful pictures of drill and lathe tool shapes but it's all right there in front of you with the fly cutter. Perhaps it's just the way my brain happens to work.
After many tries, the sound of the cutter is much improved and it gives a fair finish (my standards). The thing is that the follow up cut (back of the sweep) is very noticeable and the tool is audibly doing work. If the initial cut left nothing behind at that level then I wouldn't expect the follow up to have anything to cut off. Is it to do with the radius of the tool edge being too small for the rate of advance I use?
Or could it be a tramming problem?
I am thinking about the tilt of the column, which is 'adjustable' +/- 45 degrees; I went to the trouble of making a holder for my dial gauge and, over the 300mm length of the table, there is nearly 0.25mm difference in height. (This is around 0.05 degrees, which is pretty small, even in 'Astronomy' terms.) Over the 30mm throw of the fly cutter, I'd expect 0.025 height difference so could that account for the patterning? I don't know if it could be worth messing about with the column tilt. My 'measuring crank arrangement seem rigid and well behaved and `I have ordered a 36mm flat spanner. Can I expect to improve on the 0.25 mm I have measured.
Reviews of the mill are not too enthusiastic about the tilt adjustment on a lightweight lathe.
20880 forum posts
First thing to do is run it in both directions, if your grinding is not right or a bit blunt the tool may simply be riding up on the main cut and the second back cut is removing what it missed.
If it cuts cleanly on the leading cut and no back cut in the opposite direction then tram is a probability.
Edited By JasonB on 19/04/2020 13:10:49
7341 forum posts
Yes to both statements!
The tilt adjustment on this family of milling machines is pretty basic. On my bigger version of the same type of mill it's easy to get within spitting distance of a good tram, but downright tricky to catch and hold it on target.
Tightening mine up often causes the tram to shift slightly at the last moment. A typical sequence is 'not quite close enough', 'bit better', and 'much better'. This is followed by disaster on nipping up, with the head nudging back to 'not really good enough' and an outbreak of bad language.
First time I had to reset tram after moving the head to take an angle cut it took only 3 attempts to restore sanity. A false dawn, the second tram took far more effort - I lost count. I'm not aware there's a particular trick to tramming these machines, the problem is just making absolutely sure nothing moves on the final tighten. Patience.
Tramming is such a nuisance I avoid moving the head if possible. When angled cuts are needed, I prefer to tilt the job rather than incline the milling head.
477 forum posts
20880 forum posts
When your tram is about right you should get a finish like this where the leading edge cuts at cut through by the trailing edge ones and you get a holagraphic type effect, this mill trams at less than 0.01mm over 170mm
|Howard Lewis||19/04/2020 17:27:26|
|5036 forum posts|
When you get the machine trammed to your satisfaction, is there anywhere where you could drill and ream to dowel the Head to the Column?
Hopefully, that would provide a repeatable location, and prevent miovement when everything is tightened down.
|andrew lyner||19/04/2020 22:02:31|
|218 forum posts|
The articulation is between the column and the base, aamof, but it sounds like a good approach v- the the dwell placed at the bottom of the column.
I never met the previous user so I don't know if what I have is the best he could manage or if it just arrived like that.
@maggie - the finish in that picture was what I was getting on my road to improvement. Apologies - when I look with magnification, I can see it's not like my efforts.
@JasonB - I will have to look at my best results again (which have the same overall appearance form a distance and see if those Moiree(?) Fringes are present. I see that the front and back cuts don't appear to be very different. Perhaps a very slow feed could improve things for me.
Edited By andrew lyner on 19/04/2020 22:04:47
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