Re: [GrizHFMinimill] Opinions about mini-mill mod



Lube is important as well as a well trammed set up. The chatter can be minimized. Hard material isn't something a Mini is best at. You have to feed so slow it's not worth it.



On Friday, November 13, 2015 9:58 AM, "'Tom Kitta' tom@tomkitta.com [GrizHFMinimill]" <GrizHFMinimill@yahoogroups.com> wrote:


 
True, I didn't buy the correct mill in the first place - I didn't know any better. Now I am trying hard to correct my mistake by modifying what I have. If I fail at that - or I know there is no other way I have to try to sell the mini mill and get something bigger.
 
Fixed column is not available where I live. Besides, I didn't know any better when I bought the mill. Even now it is hard to find any review of the mini mill (I have found zero) that actually tell you what can you do with it - i.e. when using 1/2 inch end mill in mild steel the mill will shake hard when cutting anything more than 0.02 at say > 5ipm. 
 
As for my stiffening project it seems getting the column to flex less is #1 mod people do - mine is just more "extreme" version.
 
My project are not out of the ordinary or huge - like I want to make a T-slot for a small 3.5'' rotary table. Not really possible with the mini mill as it is currently - it shakes way to hard. 
 
Even though both my lathe and mill are from China, the lathe will stall before it will shake (unless doing interrupted cut) vs. stock mill which will not get the engine even working hard before super shake starts. Playing with speeds up/ down helps but to a point.
 
From: "John Lindo bechetboat@yahoo.com [GrizHFMinimill]" <GrizHFMinimill@yahoogroups.com>
Sent: Thursday, November 12, 2015 10:13 PM
To: "GrizHFMinimill@yahoogroups.com" <GrizHFMinimill@yahoogroups.com>
Subject: Re: [GrizHFMinimill] Opinions about mini-mill mod
 
 
 
Tom
Taken from your post.
"The deluxe model I have with brush-less motor has the standard super flexible column."
Super flexible,and what does that mean?just hate the word "flexible" referring to a machine tool.
 
IMHO I am not so sure you bought the correct mill in the first place.
A fixed column mill would of been my choice,and you would of already been ahead of the game actually making parts instead
of trying to make a silk purse from a sows ear.
 
Now what you have is a "deluxe,super?" drill press ,it's not a reliable mill ,when you need to do all these conversions to bring it into
something that can be called useful and rigid.
The Weiss or Grizzly (same Chinese stables) with a fixed column, tilting head, again IMHO is the correct machine to buy.
The Z axis accommodates a Kurt vise,without having to add an extension block,again that would be another area of concern to me "flexible".
It's to late for you,hoping my reply post will help future group members look around before they buy a mill ,wish you good fortunes in your modifications.
Seems you are happy with the machine of your choice from your enthusiastic post,to a point of boasting.
It's not coincidental that Tooling houses are more and more
carrying stocks of Fixed column mills,with and without the tilting head.
 
John
Spain.
 
 
 
 

 
On Friday, November 13, 2015 12:59 AM, "'Tom Kitta' tom@tomkitta.com [GrizHFMinimill]" <GrizHFMinimill@yahoogroups.com> wrote:
 
 
 
Hello,
 
1) The specific problem is same for all tilting column mini mills - the large nut at the back is held in place by a bevelled washer, it flexes a lot preventing anything beyond a tiny cut to be made, certainly far below capabilities of the mill motor. Lots of flex creates a chatter which creates lots of problems.
 
2) The forces on the engine can be easily computed - for example, a 0.2'' depth of cut in mild steel ( <200 in hardness) with .5'' cutter at 10 ipm would require around 2/3HP. The forces on the column, base, amount of flex etc. are placed are hard to find. Success may be somewhat relative to define - for example, currently with a stock setup I can maybe get 0.02'' of cut with .5'' cutter at 10ipm - would modification I am suggesting increase the performance 10x? Similar setup with pictures as proof seems to indicate answer as Yes - but I only have one indestructible with approximately similar setup.  The setup in question also doesn't mention ipm - so maybe its 1ipm cut.
 
 
3) I can easily calculate the flexing of the steel C section using engineering tool box website - but I have no clue as to how much force on the column / base milling cutter puts out in the worst case scenario. Even if I somehow knew that I don't know how the flex of the column / base flex affects the actual amount of chatter present. I think there could be a simulation possible to be programmed in but I also think this may be only done in real life for large mills. This is why I mentioned that if flex is too much I can always add ribs.
 
Added H travel and larger space for vise are a bonus.
 
In short what I am looking is someone else that has done something similar and can tell me what their experiences are regarding performance improvement. If performance improvement is huge - like around at least 5x then the change is worth it for me. If its tiny I have to see whatever I can upgrade my mill. 
 
Upgrading to solid column from LMS is out of question as I would just sell the current mill and get a larger one for a bit more $. I also think my mod, which stiffens both column and the base would produce better results - but by how much?
 
Obviously I don't want to get into a law of diminishing results - i.e. too much steel onto the project will get little additional benefit for a lot of steel - I am "feeling" my way through for that point. Maybe that point is a simple inverse T brace. 
 
Current project cost is at most 50 USD.
 
LMS solid column conversion = 250USD
 
One level larger mill - about + 400USD - depending on sale price.
 
From: "Ian Newman ian_new@yahoo.com [GrizHFMinimill]" <GrizHFMinimill@yahoogroups.com>
Sent: 12 November 2015 14:18
To: "GrizHFMinimill@yahoogroups.com" <GrizHFMinimill@yahoogroups.com>
Subject: Re: [GrizHFMinimill] Opinions about mini-mill mod
 
 
 
Hi Tom,
 
It seems to me that you are approaching this exercise the wrong way round:
 
You are saying "I intend to do X Y and Z - is this good?" - This question is impossible to answer without knowing what problems the existing setup is giving you and what your target performance is.
 
A better approach would be to:
 
1) Identify the specific problems you are currently experiencing.
 
2) Specify the criteria that will correct your problems (define the forces you intend to put on the machine, the accuracy and precision you require - without real numbers you do not know what you are aiming at and so you cannot identify whether you have achieved your goal.....)
 
3) Do the sums - calculate the dimensions of the structures you need to build in order to get the required rigidity (all you need is the Young's Modulus of steel and the second moment of area of the sections you intend to use, it is all standard engineering maths that you will find in any textbook)
 
4) Compare the performance of your proposed mods with your target and check they meet your requirements
 
 
If you just stick a load of extra bits on to your mill without having identified exactly what you want to do, how will you know if your mods were a success or a failure?
 
All the best,
Ian
 

On 12 Nov 2015, at 20:32, "'Tom Kitta' tom@tomkitta.com [GrizHFMinimill]" <GrizHFMinimill@yahoogroups.com> wrote:
 
 
 
Hello group,
 
I am interested in group's opinion regarding following mod I am planning for my mini mill. The deluxue model I have with brush-less motor has the standard super flexible column. The goal of the conversion is to significantly stiffen both the column and the base in order to take full advantage of the power offered by the motor. I also will increase the Z-travel by about 5 inches and enable the mill to have 4'' inch Kurt style vise without sacrificing any y travel.
 
To stiffen the base I plan to use 2'' by 0.5'' steel bars, welded together for 2x1 bar in a rectangle formation under the current base. The steel frame will also have "paws" extending to the sides to widen the base of the mill & these will be clamped to the bench (rather beefy one weights few hundred #). The box will extend in the back to accommodate new solid column. The old base will be attached to the new one via 4 mounting screws.
 
The new column will be made of 6'' by 4'' C steel that is around 3/8'' thick. If it flexes too much I plan on adding some ribs at the back (I don't think adding ribs to the front to make a double C will be necessary). The C column will connect to the above mentioned base with 2 screws via welded "paws" & via 3 screws to the existing base via existing 3-screw setup. The old column will be connected to the C via 6 screws and will "float" above the base. I can shim the 5 screws to tram the mill.
 
The milling head, weighting about 30# can be supported via counter weight at the back of the C. The electronics of the mill, currently at the back of the column can be moved to the back of the C or side of the C column.
 
Similar mods were done by others with great success - I just modified the materials to fit what I have available locally - I am in the middle of Canada in Calgary & thus I cannot buy much locally.
 
I just want to make the mini-mill as useful of a tool as my 12x24 lathe ... so glad I got that vs. the mini-lathe.
 
More or less I want the limiting factor to be brush-less motor power & the mill head ...
 
Ideas for improvement? Comments?
 
Tom
 
 
 
 
 

 
 




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Posted by: Steve T <std354@yahoo.com>



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