New linear glide idea

[mike hide]

I have used Teflon tape for many years here and there, wherever I needed a low coefficient of friction, monitor elevator slides and the like . The stuff comes in various widths and is about 1/16" thick with a very strong adhesive on the back of it and has been used for these kind of situations in the aerospace industry for some time

I am an ex mechanical now doing some woodworking and living on a fixed income so I am cheap by necessity, again I have followed this thread for some time. So basically I will try and build a cheap unit incorporating as many of the suggestions made on this group.

What I had in mind is having a fixed bracket on the inside of each of the gantry arms such that they support the gantry on the bed. teflon tape is then applied to the bracket where it rests on the bed . Tape can also be applied to the length of the bed. In this scheme the bed , probably MDF, would have an small overhang from the support structure that would allow an adjustable underside bracket also having teflon tape applied,this would allow any vertical slop to be eliminated . One further strip applied to the edges of the bed with adjustable taped pads would in the sides would adjust out and lateral slop. I might turn out that the lower backet adjustment could be eliminated by a light spring loading arrangement the side adjustment the same way, in fact the lower bracket might be unecessary if the weight of the gantry is pretty high

there are pros and cons to this arrangement it might be higher torque motors are required ,probably the biggest con , on the other hand iron pipe problems [sag and adjustments to the bed go away as this arrangement adjusts atomatically to any bed deformities.

[anoel]

there are pros and cons to this arrangement

Not trying to be a punk or anything... but... Dude... the only thing that is a "Pro" about that is that it's cheap... Everything else is just one big "Con". And if you really are on a fixed income... then you can't afford to throw money away, do it right the first time and you'll not wish that you had not blown the money on the first try. I've spent way more money trying "alternate" ways to build than if I had broken down and built an all aluminum, servo driven, ballscrew monster CNC machine...

[mike hide]

Not trying to be a punk or anything... but... Dude... the only thing that is a "Pro" about that is that it's cheap... Everything else is just one big "Con". And if you really are on a fixed income... then you can't afford to throw money away, do it right the first time and you'll not wish that you had not blown the money on the first try. I've spent way more money trying "alternate" ways to build than if I had broken down and built an all aluminum, servo driven, ballscrew monster CNC machine...

Well Nathan, first of all as this thread deals with wood mills I am not wishing to produce a "ballscrew monster CNC machine ", just a basic reasonably accurate machine that will produce wooden parts on a repetitive basis. all I want it to do is take the donkey work out of the process, so that I can perform the parts of the project that require a skilled effort.

Personally I could care less how much you have spent on wild goose chases, my concern is to produce a viable operating machine . Using Teflon tape in the manner I suggested was an attempt to do just that being an inexpensive solution was not the object of the exercise just a byproduct.

On your many expensive goose chases you obviously have never considered Teflon tapes, perhaps rather than dismiss them offhand you might take a second look, they are very hard waring and relatively easy to work with.
I am well aware that my hand sketches are not that elegant however you will note that the gantry load is taken directly to the bed and is centered over the bed support structure and not cantilevered off the side structure so cantilever deflections under load do not effect variations in the Z axis. In addition any local variations in the bed are taken care of automatically as the gantry bearing is riding on the bed . One other consideration ,at least in my mind is when a normal router bit is running on up sloping grain,particularly in hardwoods it tends to try and lift itself out of the cut which could in the extreme lift the gantry off the rail, the suggested design obviats this ....mjh

[ger21]

Well Nathan, first of all as this thread deals with wood mills

It's actually Joes thread about HIS machine. It's always a good idea to start a new thread with a new idea, and not take the original thread off topic.

And as for your concern about building a viable machine. I'm pretty sure that's what Nathan's trying to help you do. Bearings on pipe works well, and it's cheap. If there were a better, cheaper way than that's what you'd see here.

By all means build it and see if it works for you. If it does, great. If not, it's a learning experience.

[truman]

the thing I like about this site is everyone has ideas and they share them which usually leads to bigger and better ideas and so on and so on, the pipe and skate bearings idea in my opinion was one of the great ideas that opened the door for many of us to try and build one of these wonderful contraptions, and I hope Joe and mike hide and all of the thinkers out there keep up the great work and never stop pumping the great ideas out the more the better. Sorry Joe I had to say something

[anoel]

Yeah, don't listen to me... build your machine, piss money away. I have built two machines that uitlized Delrin slides on aluminum frames and both funtioned to a degree but ultimately were not rigid enough to handle any "real" tasks. My current machine is using real linear bearings and shafts. And rigidity is still an issue.

And that whole variations in the bed will reflect in the gantry bit... Ummm variations in any of the axis are what makes for a poorly functioning machine, you'll have to keep components loose enough to overcome those variations and you'll have "slop". Again build it, put a bit into the spindle and pull and tug on the bit and watch how even a small amount of force makes your machine flex to a great dregree. You'll then realize that I wrote earlier to help you out. Ger21 saw it right off and I wasn't even talking to him. If I ever post a bad idea, I hope that someone points it out to me in a manner that I can understand before I execute it. I'd hate to waste time and money into something that others know through experience will not be successful, no matter how successful that I think that it will be.

[mike hide]

If you are looking for rigidity then go ahead and but a $100,000 + milling machine that weigh many tons ,thats why they are so heavy and hefty. If you want even better performance encloseit in a temperature and humidity controlled enclosure like most jig boring machines are .

The machines we are talking about are wood mills . Trying to hold consistant tolerances to better than a a thousanth or two is going well near impossible which for the most part is unnecessary anyway when dealing with wooden projects .

[ger21]

Trying to hold consistant tolerances to better than a a thousanth or two is going well near impossible which for the most part is unnecessary anyway when dealing with wooden projects .

Try even getting to .005.

[aggie_67]

Anoel,

Your last post read "Yeah, don't listen to me..." Based on your posts don't think anyone will be. Need to stop acting like a high school skater "dude" and make more mature helpfull comments.

[anoel]

???? I offered Mike a little "real world" advice about his machine... I don't think anyone can dispute the fact that my advice was sound and not without personal experience to back it up. Mike just did not like the fact that I spoke out against his "design".

(Ger, I'd guess no better than .015" with poor repeatability.)

[mike hide]

My post regarding the use of teflon tape was not intended to ruffle feathers only to offer an alternative solution . Furthermore I don't mind it being shot down, but lets do it based on sound engineering reasoning not rhetoric.

Giving some thought to the black pipe/skate bearing design, there will be some variation in the Z axis over the width and length of the bed due to slight variations in the pipe set ups not being perfectly parallel with the bed ,sag between supports etc. To try and alleviate this situation I was thinking that perhaps once the machine is operational and set up whether it might be a good idea to atach a dial gauge to the gantry and run it over the bed in the X and Y axes observing the variations . Then run a cutter in the router set to the maximum variation and then skim the entire X,Y surface, in effect zeroing it out,just a thought...mjh

[aggie_67]

Appreciate your thinking outside the box, that is how progress is made!!

As to the thought of skimming out the variations, it may be one of those things that sounds good in theory but actual practice rules it out. The problem as I see it is where as this technique would hae the bed routed true on a point by point basis, your work is not mounted on a point by point surface. It is controlled by how it is mounted; example if your bed axis had a saging curge (highly possible) then routing the bed would put a curve in the bed. Then if you mounted a piece on the 4 corners it would not touch the bed in the center.