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  1. #1
    Join Date
    Aug 2016
    Posts
    13

    Replace T-Slot for tooling plate?

    Hello,

    My machine(1st image) is based on T-slots but I found the joint section of each T-slot may not have sufficient flatness for PCB milling. I am thinking abut ordering a tooling plate for replacement. What are the pros and cons of T-Slot and tooling plate? Which one is better?

    Poting






  2. #2
    Join Date
    Nov 2012
    Posts
    1267

    Re: Replace T-Slot for tooling plate?

    Flat table alone is not enough, the machine would have to be perfectly trammed. An easier option for milling PCBs is using a spoilboard.

    Attachment 330894

    Attachment 330896

  3. #3
    Join Date
    May 2005
    Posts
    3920

    Re: Replace T-Slot for tooling plate?

    On a lot of these T-slotted extrusions you need to understand that they where never meant to be a replacement for the type of T-slots seen on a milling machine. The profiles often have very specific non flat surfaces supposedly designed to aid in keeping the assemblies together. In other words not all T-slotted extrusions make for good machine tables for direct mounting of parts.

    In a router it is pretty common to see the use of waste boards to provide a flat surface to work on. This is one approach to deal with the mounting of work pieces. In the context of a printed circuit board you might want to consider the possibility of a vacuum hold down assist. There are several issues with PCB material that have to be recognized for successful milling. One is that the material does often sit completely flat. The other is that the material varies dramatically in thickness.

    Both of these issues can lead to problems where more material gets removed than is desired which can lead to tool breakage. Imagine a tool flying over hilly ground running into the peaks. An exaggeration of course but if you are using really tiny end mills it can be a disaster. In any event if PCB work is your primary goal I'd focus on holding approaches that draw the board down and keep the board as flat as possible.

    If your goal is a more general purpose machine then by all means consider a tooling plate. The problem here is there is a 101 ways to go about this and in the end you need to choose what is best for your operations. In some cases pulling the extrusions and replacing them with a thick and heavy tooling plate is the right answer. Other times bolting a thinner plate to the extrusions makes sense. On top of all of those you have the prospect of interchangeable tooling plate systems, vacuum tables (not to be confused with suggestions for PCB making) and other fixturing devices.

    So in the end you need to work out what is best for you and your intentions. In some cases buying a cast iron table with real machine tool T-slots makes sense. Of course in all of these approaches there is an assumption that you can mechanically align you machine to the point it is square and parallel to the table/plate of your choice. Sometimes a waste board approach makes a lot of sense though they aren't usable at all if you intend to do anything requiring coolant or lubes.

  4. #4
    Join Date
    Aug 2016
    Posts
    13

    Re: Replace T-Slot for tooling plate?

    Quote Originally Posted by CitizenOfDreams View Post
    Flat table alone is not enough, the machine would have to be perfectly trammed. An easier option for milling PCBs is using a spoilboard.

    hi,
    Spoilboard is the first thing pop-upped in my head. Due to the unevenness of the low quality T-slots on my machine, I think the position where the spoilboard was made needs to be marked or remembered. I guess any movement of the board will make difference if you know what I mean. Can you recommend any tool bit for making spoilboard? I searched and it came out something like "2+2 Design router bit" (Here). It looks nice, but I was shocked by its price. I'm new to the CNC world. Thank you for the input.

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  5. #5
    Join Date
    Aug 2016
    Posts
    13

    Re: Replace T-Slot for tooling plate?

    hi wizard,

    Thank you for the detailed information. I've heard of vacuum table, but I think I will use double tape first. BTW, I've seen someone who designed a holder for 2 toothbrush heads around the spindle which will then "push" the board onto the surface where the tool bit goes. (Here).

    Frankly speaking, I like tooling plate more. Simply by its appearance. It's flatter and more like a serious work to me. I am still waiting for the quote from the manufacturer. If the price was right, I'd invest a tooling plate.

    Poting

  6. #6
    Join Date
    Sep 2006
    Posts
    6463

    Re: Replace T-Slot for tooling plate?

    Hi, even if you use a thick piece of "flat" aluminium plate with tapped holes you'll still have to use a dial indicator and shims to make sure it's laying flat.

    MDF can be skimmed with a simple HSS fly cutter to make it flat and level........whatever cutter you use, it also needs to be rotating square to the table surface or you'll get ridges on the surface as one side of the cutter digs in etc.

    Not knowing the design of the router, I would suggest that if the T slotted table extrusions were completely removed.......(if that is possible without compromising the strength of the machine frame)....... and a 20mm thick aluminium slab is bolted down in it's place, you could probably save a lot of money by just marking off the holes in a grid pattern and drilling all of them on the machine but only tapping them as needed.

    Tapping with that router is not possible under power, so the holes would need to be tapped by hand, or off the machine with a tapping head on a drill press.

    Once the aluminium plate is bolted to the frame and shimmed to make it lay flat, the surface will most likely need skimming lightly to make it dead flat as it's highly unlikely that it will be dead flat in the raw state........the router with a fly cutter should be quite capable to mill the surface flat with a shallow DOC.

    If you opt to just put an aluminium plate on top of the existing Tee slot table you'll lose 20mm of Z height.......probably the simplest way to go if the height is not a problem.

    The draw back is, with the plate laying on the Tee slot table top, it will soon get the holes jammed full of swarf, whereas if it replaces the Tee slot table the holes will be through and clear.
    Ian.

  7. #7
    Join Date
    Aug 2016
    Posts
    13

    Re: Replace T-Slot for tooling plate?

    Quote Originally Posted by handlewanker View Post
    Hi, even if you use a thick piece of "flat" aluminium plate with tapped holes you'll still have to use a dial indicator and shims to make sure it's laying flat.
    That's a very good practice. I will order the dial indicator for sure. Using the indicator, shims and spoilboard seems to be the best solution for me. Thank you, guys. I know I come to the right place.

    Poting

  8. #8
    Join Date
    Aug 2016
    Posts
    13

    Re: Replace T-Slot for tooling plate?

    I just got the digital indicator and holding arm. It turns out the error in flatness is way beyond the requirement for PCB milling. At this moment, I only measure along the Y-axis. I think X-axis is uneven to some degree, too. A spoilboard is definitely required. BTW, is there any accessory that can turn my indicator into a co-axial indicator? The spindle has ER11 collet chuck (7mm max).






  9. #9
    Join Date
    Sep 2006
    Posts
    6463

    Re: Replace T-Slot for tooling plate?

    Hi, the run out is to be expected with these extrusion based bolt together machine type constructions.........replacing the table with a solid piece of MDF or 20mm thick aluminium will make it better.......the MDF will need to be re-surfaced occasionally as the surface is sacrificial.

    The 20mm thick aluminium approach would still need to have an MDF board on it to act as the throw away bit so replacing the original extrusion table with aluminium would probably be a waste of time, but that would be my preference as I like a nice hard base to work on that can be made flat and accurate......the MDF only needs to be a thin layer in that case.
    Ian.

  10. #10
    Join Date
    Jul 2011
    Posts
    35

    Re: Replace T-Slot for tooling plate?

    Here is my solution to the problem :
    Attachment 331810
    This works especially well for larger series : I mill out a pocket slightly larger than the PCB. Then I know it's flat and perpendicular and I can even reinsert the PCB a second time in exactly the same position (first past isolation engraving/milling with the V-bit, second pass drilling with say a 1mm carbide drill)

    Note : the bolts holding the PCB go through the MDF and fit exactly in a set of T-nuts. I measured this out accurately and after milling out the square with a 6mm mill I let the mill drill to 17mm (MDF is 18mm) and then by hand broke through the bottom of the MDF into the T groove.
    I slid my T-nuts under the MDF using a piece of copper wire to push it in the right position so the bolts could go through. The large washers overlap the PCB on the corners by about 2-3mm, enough to hold the PCB down. The sideways movement is already prevented because the PCB is sitting in a recessed square in the MDF (which is milled to thickness of the PCB - 0.5mm for optimum clamping)

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