Work holding - CNC

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supertom44

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I'm curious what methods people use for work holding when cnc machining.

I was using some double sidded tape last weekend and ended up wasting multiple bits of wood due to the tape failing.

I've used super glue and blue tape before which works well, but feels a bit of a faff.

I've used some side cam clamps in my old machine which worked pretty well, need to try and make some for my current machine which doesn't have the threaded inserts that my old one had.

Not a fan of the hold downs as I once ran into one with the bit :(
 
The question is too nebulous. A more or less appropriate work holding solution hugely depends on the work being held and the operation being perfomed.

Describe some things you want to cut.

A base board to your router that you treat as a consumable item opens up many more possiblities than one you wish to remain pristine.
 
It was more of a general question on what methods people use, than for a specific project.

Last weekend I was attempting to cut some french cleat brackets out of 18mm plywood, this weekend I'm going to attempt to carve a logo into some wood (yet to be determined which type) coasters.

I like the idea of attaching a sacrificial layer, gives me options of either screwing/nailing or even adding threaded inserts etc.
 
I have a base layer on the CNC with an array of threaded inserts; so I can bolt holddowns/clamps or stops into the surface. It works OK, but sometimes I do just put a screw through the workpiece into the base board.

Vacuum holding is really good if you're not cutting through the workpiece.

I've only used the tape and glue method a few times, but it seems OK for light machining.

Basically, horses of courses; it totally depends on what you're making.
 
It is a total mishmash for me, I use the masking tape and superglue method often on smaller things.
It is way better than any double sided tape I have ever tried, also easy to remove and very strong. I get Q1 yellow tape from the car paint shop, I do think the quality of the tape makes a difference.

If its a big sheet I just use screws but sometimes this can be a problem as the middle can rise up a little if you can`t get a screw in it due to the design, the solution is a bit of tape and glue in the middle.
You should always have an mdf base anyway in case you need to cut through.
I have a vacuum pump waiting for me to machine up a vacuum bed but I haven`t done it for several years so it must not be that important.

If I am doing a bunch of stuff like your example of coasters I just make a little jig for alignment which I screw down and use tape and glue on the material.
If doing loads then I might bother to put an over centre side clamp on the jig.

Ollie
 
masking tape and superglue usually for me

I have used screws into sacrificial board as well, but mostly tape. The 3m tape is on offer this weekend at Lidl, so i'll be stocking up. Especially as I now have the parts to fix my CNC.
 
ive used the masking tape method, traditional hold down clamps, i swapped the metal parts for hardwood so if i hit it by mistake its no big deal,and yes i used to screw everything into the spoilboard. i have a new cnc and am thinking of fixed positions with a more or less permanant stop on 2 sides, then wedges and dogs on the other 2. a lot depends on your stock thickness, how much material is outside the cut area, if you are light v carving or cutting right through. i may even make a small vacum pod powered by a shopvac i can add for some projects, theres several examples on you tube.
 
For one or two bits I use cheap masking tape from Wickes and CA glue but for repeats, I cut a 'cap' and use socket screws into threaded inserts. I've never used tabs as I prefer to leave a 0.1 skin on which has so far never failed me.
 

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I have a spoilboard on the machine and will happily use screws to hold the job down.I do make a point of using brass screws because in the event of an oversight,they can be cut with little damage to the cutter or machine.Hardened steel screws give off lots of sparks-guess how I know?I will use packers and screw down wooden clamps if necessary and I then make a point of choosing a retract height to clear them,with brass screws as the clamping force applying mechanism.I'm no fan of double sided tape and would rather clean off a few tabs than re-cut a piece because the tape let go.I think its only a technique for small low power machines in any event.

If I do have to make three or four of the same item I tend to screw short pieces of wood to the spoilboard for location and add a few wooden clamps to hold them down.It gets a bit more awkward if I have to cut the outline but it can be done with patience.

I have doubts about vacuum systems for hobby machines but think them great for industrial size jobs.The thing that I can't overlook is that a good commercial system will pull a good vacuum through 18mm MDF.I don't know of a high flow pump that will operate off a domestic supply and a low flow,high vacuum pump of the type used for bagging glue jobs doesn't tend to have the capacity to overcome the leakage inherent with man made boards.It wouldn't be hard to design specific fixtures from plastic sheet material to cope with a run of parts of the same type but who makes dozens of the same thing in a hobby workshop?
 
I saw a video of someone using plastic brad nails to secure workpiece to spoil board. Didn't know these existed, anyone tried them ?
They are from one specific company, I forget the name now but its a special nail gun as well ( green if I remember) so I don't think you can just use them in a different nailer.

Ollie
 
With the plastic nails, you would need to consider if you wished to remove them afterwards, and if so, how you would do so.

Tacwise sell them and seem to imply they work with their guns. The green gun is Omer (Raptor Plastic Nailers)

The idea about brass screws above is good. This is just to note that aluminium and nylon are also available.

If you do use a sub-base with threaded inserts, consider recessing them a little, so the cutter can touch the sub base without damage.
 
I run a CNC with a 2KW water cooled spindle mainly machining oak ash and beech.
It is in a production environment some items being 600mm square and small batches to small plaques and signs in batches of up to 1500
I am in no way conservative on my feeds and speeds
The only method i use is Blue tape super glue and activator.
Vices get in the way as do clamps
Vacuum is only suitable on larger items anything under about 125mm square is very hit and miss coupled with the cost of a well specked vacuum pump
Screws and nails leave marks and damage in the item
Tabs can be useful but on complex items a fair few can be required and then there is the extra work of removing them and cleaning up the edge of the piece
In the past 3 years I have tried all of the above and return to the glue and tape
I have spent a lot of time and trial and error trying various tapes, glues and activators and have now settled on my preferred brands with good discounts set up with suppliers. earlier today I collected 100 x 50ml bottles of medium super glue
I use moisture resistant mdf as a spoil board and skim it with a carbide 50mm cutter when i need to i also have a selection of 20mm dog holes over the spoil board which i use removeable dogs in to align raw material of for 2nd op processing.

Hope this helps

D
 
I run a CNC with a 2KW water cooled spindle mainly machining oak ash and beech.
It is in a production environment some items being 600mm square and small batches to small plaques and signs in batches of up to 1500
I am in no way conservative on my feeds and speeds
The only method i use is Blue tape super glue and activator.
Vices get in the way as do clamps
Vacuum is only suitable on larger items anything under about 125mm square is very hit and miss coupled with the cost of a well specked vacuum pump
Screws and nails leave marks and damage in the item
Tabs can be useful but on complex items a fair few can be required and then there is the extra work of removing them and cleaning up the edge of the piece
In the past 3 years I have tried all of the above and return to the glue and tape
I have spent a lot of time and trial and error trying various tapes, glues and activators and have now settled on my preferred brands with good discounts set up with suppliers. earlier today I collected 100 x 50ml bottles of medium super glue
I use moisture resistant mdf as a spoil board and skim it with a carbide 50mm cutter when i need to i also have a selection of 20mm dog holes over the spoil board which i use removeable dogs in to align raw material of for 2nd op processing.

Hope this helps

D
Thanks for the info, I'm going to give tape and super glue another go on my next project.

What's brands have you settled on?
 
3m tape for me. Its on sale at lidl right now
Everbuild superglue and activator - cheap as chips from amazon or toolstation
I use everbuild too, mainly due to the fact you can get it in larger sizes.

Didn't realise they stocked it at toolstation this is very convenient, cheers.
 
Thanks for the info, I'm going to give tape and super glue another go on my next project.

What's brands have you settled on?
I use Everbuild medium glue 50ml size shop around for it I pay a lot less than Amazon and Tool Station prices but i do buy a box of 20 at a time from a local tools and fixings supplier

Bond It activator as its available in larger cans

50mm blue UV resistant tape from Essex packaging Supplies, its well priced and the right amount of stick, some of the bigger name tapes I have used have delaminated MDF and also pulled soft grain from wood

I transfer the glue into a small squeezable bottle with a micro tip it really cuts down on the amount used
I blow the spoil board off with an air line and usually run a small rubber roller over the tape on the board prior to applying glue and the workpiece

I am not far from you if ever you want to drop buy
 
It was more of a general question on what methods people use, than for a specific project.
It depends on the job but in my own learning, I found workholding was absolutely key to decent work. For thin sheets of material I regularly use 3M painter's tape, which provides a very good hold with easy removal when coupled with a viscous CA glue without activator spray. I like the ability to move a workpiece a little after first applying it to some sacrificial MDF and not using an activator gives me twenty seconds to make adjustments to position.

Clamps may be used, depending on the cutter size and the operation on the workpiece. Material hardness may play a part so cutting MDF (preferably don't because it is just glue held together with dust) is different to carving an intricate 3D pattern in Maple wood. Clamping may help with two sided cutting too but accuracy of positioning will be vital.

I tend to mainly use pairs of modular vices which I can position anywhere and at any distance from each other on my baseboard and lock them into position. My baseboard was modified from the original MDF item supplied with the machine to an aluminium baseboard with M6 threaded holes placed at 20mm intervals from each other. It was a very expensive modfication but it improved rigidity and accuracy and I can reliably machine metal to ±0.001" now.

I found MDF was not able to reliably support threaded inserts, which is how I first started trying to improve my workholding options. The insert holes would stretch and there was movement in the clamping arrangements after prolonged use. I have also used the valchromat MDF and dog holes with side clamps (UJK) for a while. Eventually, I went for a 12mm thick aluminium baseboard (sea of 840 holes) and I have never regretted that decision. I think that the holes provide a more uniform clamping environment than tracks can and its repeatability is better by dint of the accuracy of the hole positions. The baseboard, stiffening rods and modular vices were all supplied by Saunders Machine Works in the USA.

EDIT: to add image of simple clamps holding a small MDF jig for laser engraving items.
 

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