Development Of A Frame To Hold The Makita 2107F Portable Bandsaw For Horizontal Cut-Off Use
I am developing a frame to hold the Makita 2107F portable bandsaw in a horizontal position to allow easy cutting off of bars.
This is a CAD drawing – still work-in-progress- illustrating the concept:-
Click on the image to see a larger version.
A Major Problem Surfaces
The above concept looks promising. I knew that when the saw is raised to the top of it’s strock – blade touching the top of the bar being cut off that the capacity of the saw would reduce. Similarly as the saw drops to the end of the cut the capacity will be reduced further.
What surprised me when I made these movement plots was how great the reduction in capacity was:-
- Capacity in horizontal position – 120 mm
- Actual capacity taking into account the swing of the saw – 76.6 mm.
This is illustrated in the next image:-
Click on the image to see a larger version.
Note that in the above image I have only shown the swing of the saw itself. The horizontal arm also swings accordingly but to keep the drawing clear I have not shown that.
How To Avoid The Reduction In Cut-Off Capacity Of The Makita Horizontal Bandsaw Frame
Three means to reduce the effect of the swing of the arm from top to bottom spring immediately to mind:-
1. Make The Arm Longer.
This is easy to do but has issues of rigidity.
The arm is acting as a strut – the Makita 2107F bandsaw blade moves towards the person holding the bandsaw, ie away from the swinging arm. Since this puts the arm in compression it has to be of large section to take the compressive forces. Shorter is better for compression.
This compression effect is illustrated on the Makita Bandsaw Review page where there are photographs and videos of the prototype.
I think making the arm longer is the best and simplest option. I’ll be using CAD to see how long the arm has to be to keep the reduction in capacity to a minimum.
One thing I am acutely aware of is weight. If the arm is made long and very beefy (to take the compressive forces) the weight may force the bandsaw into the cut too hard and cause issues with saw-blade life and perhaps motor overload.
Further Thought On Weight Of The Arm
Since writing the above and as I was investigating the effects of different arm lengths the following two thoughts came to me:-
- Another problem with a heavy arm is that the weight will put a strain on the bolts holding the arm to the bandsaw itself. The bolts will take the strain but it will be putting undue stress on the tapped holes in the bandsaw and on the bandsaw frame itself. Being made of light alloy I want to avoid putting heavy stresses on the tapped holes and the bandsaw frame.
- An obvious solution to the problem of excessive weight of the arm is to counterbalance it! So simple and that’s what I’ll be doing.
The only constraint on the length of the arm is now the strength in compression and practicality of having a very long machine.
By the way when I talk about compressive strength of the arm I’m not referring to the buckling strength ie the force required to bow or buckle the arm. I’m referring to rigidity in compression. If you look at the first video of the long-arm Makita bandsaw frame prototype you will understand what I mean.
2. Make a Parallel Action Arm
I could make a pantograph type arm that would keep the saw horizontal, but there would still be some reduction incapacity due to the swing of the arm.
A simpler way to achieve the same result would be to hinge the saw at the point of it’s connection to the arm. The saw would then have to be held in a horizontal position by the operator.
Since I hope to make the bandsaw act as a set-and-forget tool, this is ruled out.
One way to make the saw travel vertically only would be if some form of parallel motion was devised as in the Watts parallel motion used on Beam Engines. Far too complicated!
3. Eliminate The Arm – Mount the Saw On vertical Slides.
The saw could be fixed to bushes that slide on vertical slides thereby keeping the saw in one horizontal position.
I can see issues with friction and the bushed binding on the slides.
Next Step – Investigate Increasing the Swinging Arm Length
The next step in the development of this design for a frame to hold the Makita 2107F portable bandsaw in the horizontal position for cut-off of bars is the investigate how long the swing arm needs to be and how strong in compression it can be sensibly be made.
I made several increases in arm length and each time the cutting capacity increased.
At about the same length as seen in the first prototype movie (674 mm) the capacity increased to the maximum of 120 mm.
It seemed like this would work. But then I had a suggestion from George, my friend and fellow model engineer in Thailand.
Dropping The Pivot Point Of The Makita Bandsaw Holding Arm
George suggested dropping the pivot point of the swinging arm.
I tried this in CAD and the results and reason for them were immediately obvious.
By retaining the original short arm (length 333 mm) as seen in the drawings above and dropping the pivot point, the capacity increased to 110 mm.
This is seen in the drawing below.
Click on the above drawing to see a larger image.
Also you will see that by dropping the pivot the length of the vertical upstand has reduced making it stiffer in bending.
Of course the arm itself needs an angular strut to strengthen it as shown above.
Clearly this is the way to go.
Update 29 Dec 2013 – Outline Design Almost Complete
The concept design for the Makita 2107F horizontal bandsaw frame is nearing completion.
There are plenty of details to add but there is enough of a design complete to make a start on fabrication.
I can work out the materials I need to make the frame and go out to Pak Chong to buy them.
Click the images to see a bigger version (Opens in new window)
This is the same drawing of the Outline Design For The Makita 2107F Bandsaw Frame but with the Makita portable bandsaw itself hidden:-
Above is the outline design drawing of the Makita 2107f horizontal bandsaw frame. This is what will be fabricated.
There are more details to be worked out but the basic frame design is there.