Mobile Saw Base - What Size Wheels?

[aiyou]

Seeing BeauxTi's thread about mobile bases got me thinking again about my plan (seems all I do is plan, but that's a story for another day)..what size wheels would be most appropriate?

At this point, my plans will probably settle somewhere around the following:
- base length = 38"
- base height (including wheels) = 24" (total working height ~38", as that is what I'm at with the stock BT3100 base)
- base width between 22" and 24"

I have a set of Peachtree 4" castors (two locking swivel, two fixed).

When working in Sketchup, and adding in the wheels (with their overall height of ~5 1/4"), I got to wondering if I should not be using smaller diameter wheels, and if so, what? Would a lower center of gravity be better, or should I be okay with these?

Saw is sharing space in garage, and will only be moved across concrete surfaces of the garage and driveway.

Thanks
Rob

[greenacres2]

3" casters would likely be sufficient, since you already have the 4" and the base will be a little smaller than the footprint of the saw top (including rails), you'd have the room to bring the casters--at least the locking swivel--outside the base. Kind of like the Shop Fox universal mobile base. This would enable you to drop the cabinet just a touch.

earl

[LCHIEN]

bigger wheels roll smoother and more easily. Think about the wheels going over a .5" step which has to climb proportionally higher and where the step hits the circumference of the wheel. I'd go with 4" if possible, it depends on if your floor is perfectly smooth or maybe you'll have some wood chips or uneven-ness or stuff you have to roll over...

As for COG, a smaller wheel diameter doesn't lower the COG... COG is NOT the center of the wheel, its the center of mass of the whole assembly. Unless you lower the overall height of the unit, or arrange it so that the weight is positioned lower, you won't be affecting the COG any. Lower COG implies more stability, less likely to tip over.

As long as you keep the weight centered between all the wheels and not too tall the COG will probably be OK.

[cwsmith]

As mentioned by Loring, the larger the diameter the smoother they will roll. So much depends on the weight and of course the surface of your floor.

My BT 3100 utilizes a Herc-U-Lift, which has 3" diameter wheels. My floor is basically plywood and it rolls very easily. But the wheels themselves mount up the legset, so the leg pads themselves are only and inch or so above the floor in the lifted position, thus maintaining the original design height of the saw (38") when "fixed" for operation.

When building my router table, I mounted it's 3" lockable wheels on a cross-support between the table legs. While the wheel locks are adequet for some operations, the wheels themselves don't offer a lot of friction surface. Thus having the wheels mounted higher, keeps the legs fairly close to the floor and therefore I can "wedge" them, should I need to feed something of more weight.

My much heavier HF tool chest came with 4" wheels, two swivel and two fixed as you describe your intention. However, I found that chest much less manuerverable in my small little overstuffed shop. I quickly opted for all "swivel" wheels, which works much better for me.

I hope this helps,

CWS

[mpc]

My much heavier HF tool chest came with 4" wheels, two swivel and two fixed as you describe your intention. However, I found that chest much less manuerverable in my small little overstuffed shop. I quickly opted for all "swivel" wheels, which works much better for me.

I have the exact same issue with my HF roll-around cabinet. It's almost impossible to fit it between other existing cabinets since it can't be rolled straight back... gotta wiggle it like parallel parking a car. I too plan to swap in casters one day... just dreading the job knowing how heavy the empty cabinet was let alone what it weights full. It'll be a mind-bending challenge to raise it enough to safely work on it. Perhaps my engine hoist?...

My BT3000 sits on a Delta mobile base: two fixed wheels in back and a single centered caster in front. So maneuvering it out of its wall storage area means a lot of zig-zags too. That mobile base will get replaced with 4 casters when I make a totally new under-saw cabinet in the near future.

The material used for the wheels has a big effect on how well the wheels can grip the floor when locked. Harder wheels are easier to roll typically but they'll slide more easily when locked. When making things mobile, the basic questions I ask myself are:
1: will this item be subjected to a lot of fore/aft forces (i.e. will I be moving heavy workpieces over the tool, or will the work I do create a lot of forces - like hand planing stuff on a workbench)? If so, having the original tool legs on the floor is what I plan. For my workbench I glued on strips from a computer mouse pad to aid the grip on my cement floor.

2: will there be a lot of vertical forces - hammering/pounding? That'll wear out casters fairly quickly. Legs on the floor again...

If those two questions are "no" answers, then 4 double-locking casters get used. Most of my "bench top" tools are actually mounted to roll-around cabinets. They're roughly 25 inches along one side and either 15 or 30 on the other. With doors on the 25 inch side so I get lots of storage space in addition to having one less tool on the bench.

For balance or "center of gravity" concerns the wider you can space the wheels the better. Many tools have work surfaces wider than their base (e.g. jointers) so putting the whole tool on a platform lets you move the wheels much further apart (imagine the jointer on a skateboard) for stability... as long as the platforms+wheels don't become tripping hazards while you work! For tall items like band saws the typical footprint is rectangular. If you do most of the rolling in the direction of the longer side it'll be more stable. Cleaning the floor before moving/storing the tools, especially those that are tall & more tippy, will reduce the tip-over risk by reducing the chances of something jamming a wheel.

mpc

[cwsmith]

MPC,

Regarding your HF tool chest. Mine is the relatively inexpensive 11-drawer, 3-piece unit. You may well have much heavier tools than I do, but once I removed the automotive socket sets and wrenches from the top chest, I was able to lift it off and set it on my bench. The second chest was easier to empty and the bottom just contains useables like wrags, mineral spirits, etc.

Changing the casters would be much harder if you aren't able to flip the bottom cabinet over, bottom up.

I put the two lockable casters on the front, rather than the end. That way, with the two new swivel casters in the back, you can easily move the chest around the shop and then roll it back into a fairly enclosed position against the wall. With the lockable caster in the front (drawer side), they can easily be locked into place.

Now the question is "what to do with those fixed casters?" (BTW, HF has matching lockable, swivel casters which properly fit the bolt pattern of the base cabinet.)

CWS

[mpc]

My HF chest won't be quite so cooperative... it's one of the US General roller cabinets (HF item #68784). Empty it weighs more than I do. As big as my woodworking bench too. Lots of great storage - it really came in handy since I'd just moved and needed a big place to store stuff that normally lives in wall hung cabinets... I needed to insulate and drywall the new garage before I could even think of replacing the wall-hung cabinets. HF put this puppy on sale at a perfect time; a friend with a pickup bought one as well so HF fork-lifted 2 of em' into his truck; we unloaded them one by one. And with two of us it was still a challenge!

Then he went and lost the keys to the locks for his by the next weekend! his wife gave him no end of grief for loosing them so quickly.

What to do with extra non-castering wheels? Got a big library? Make one of those ladders that runs on a track around the library. haha... Seriously though, I've considered making a custom "mover's dolly" that steers like a child's wagon: 4 regular wheels with two on a pivoting link attached to the handle I'll use to drag this thing around. I have a stack of boxes full of books still unpacked... waiting for the day I finally get around to making shelves & a desk for the office room. This flat wagon/dolly will use up some shorter 1x4 scraps and some wheels. The idea actually came from some of the "mobile base" units that use a 2-wheeled handle+hook setup to grab-n-drag heavy tools.

mpc

[aiyou]

Thanks all for the input.

I have the Herc-U-Lift now, and its been adequate, but I want to move away from the splayed legs and gain some storage.

Other than the height of the wheels, the biggest concern for stability that I had was the (what appeared to me when drafted in SketchUp) relatively short distance between the front and rear wheels. Given that I'll have nearly 5 inches below the base of the cabinet and the floor, perhaps I could build a shallow box and add some additional weight (sand, mdf, scrap metal, etc) to aid in tip-prevention.

Spent today steam cleaning the lower level of the house..now I know why I just keep working on plans, and never see sawdust...oh, well..perhaps next weekend.

[vaking]

BT3100 stands natively at 38" above the floor but it is the tallest saw I know. Other saws are lower, for instance Delta Unisaw stands 34.5" tall. Make the saw height what you like, not what original was. I like the height of kitchen countertop, so I made my saw 36" high like the kitchen standard.
My base uses 5" wheels. I had those already, they were industrial duty and I used them. Base is very heavy when loaded but rolls well. I have saw with extended rails, full length of rails is 84", length of base is 72". Depth of base is 24". Rails overhang the base by 4" on the left and 8" on the right.
The space between the wheels should be occupied by a torsion box. Such box adds strength to the base, without it base will sag. I built without a torsion box and lived to regret it. I put in steel beam underneath the base to compensate but torsion box would have been better. Search this web site for torsion box, I believe you will find info. I remember a very good article by Ray Girling about the base, not sure if that article is still available.

[LCHIEN]

aiyou, I'm thinkng you are overthinking the COG issue.

A saw with the square metal stand legs (BT3000) would be the comparison point... I have never heard anyone complain about its tippiness or stability.

Stability is improved by moving the COG lower or moving the support points where they touch the ground outwards (farther from the COG).
A BT3100 with the legs splayed out a bit would have more stability than a BT3000 on its stand, but then again, I've not heard any complaints about the BT3000 stability.

So a wood-base would be heavier than a metal base and add mass low to the base would lower the net mass center so a wood base support would improve stability if you left the wheels at the same points as the feet of the metal stand, or wider. Don't forget to allow for offset swivel wheels - the point of contact moves inwards if the caster is swiveled so its under the saw, resulting in less stability. If you plan to use swivel wheels then you should move them outwards a inch or 2 to compensate.

[aiyou]

Alex -
Thanks for the reminder about the torsion box. I know I've considered them in the past, but certainly didn't put two-and-two together when thinking of adding a box below to hold the add-on weight....certainly can address two needs with a single solution.

Loring -
Good point about the BT3000 base being a good comparison. Overall height will be similar, and the cabinet slightly longer, but I'm still going to stay within the footprint of the stock saw (no extension rails at this time due to space).

Plans will likely be based on a modification of the slant-front tool chest from ShopNotes issue 79. Basic dimensions are 28" (l) x 19" (w) x 35 " (h) with the same 4" casters. A loaded tool chest might have more weight, but probably not by much. So, if that's stable enough, I should be okay.

Thanks all for your input.

Rob

[RAFlorida]

For our BT3000, I used 4" casters and found that size to do very well on the torsion box base. It takes the saw to where I need it and then lock all four casters.